We've always spent a good deal of time, when introducing them to the pool, showing the dogs where to get out at the steps or bench which is in the shallow end. Most dogs, even retrievers and other water dogs resist getting into a pool even if they are used to swimming in lakes, rivers, streams, ocean so you actually have to make many of them enter the pool. We start them out gently with one person in the water pulling and the other pushing. All our dogs have been large and GIANT. We then hold them like a child and allow them to move their legs. Some calm down pretty fast; others it may take a week or two before they become comfortable. Then we gently let go, holding the collar and let them swim around a few circles and then we guide them to the steps always. For a while they will resist getting in and some will avoid you if you are too near the pool. In the beginning we also guide them back and forth between the steps and bench, letting them get out at each place occasionally.
Once they are somewhat comfortable swimming we have them get in the deep end (sometimes they need a push but not a surprise one) and then call them to the steps. We do this until they show no interest in trying to get out any where else.
The first few weeks one of us always sits out with them ready to call them away from any place other than the steps when they try at an inappropriate spot. After about a month I let them out and do some chores keeping a close eye on them.
One thing that helps is to get your dog fetch "crazy". They are more likely to jump in after a favorite toy, or fall in. But only do this when you are there to assist and calm them, at first.
We have a particular situation with three puppies who jump on top of each other. So for several months I watch them particularly closely. Ours started swimming this summer and I still keep a pretty good eye on them. On rare occasion one will get a little freaked when he cant' get a particular floating toy after several attempts and another jumps on top of him. That's about the only time mine have tried to get out at an edge but calling them to steps gets them going in right direction.
Some dogs have bodies that make it easier for the back end to have buoyancy. Many breeds don't. My Labradoodles hardly have to paddle with their rear legs unless they are racing for a toy or wanting to go fast for any other reason. On the other hand my Mastiff puppy has a rear end that definitely doesn't have much buoyancy so he has to paddle continuously with his rear. He is 11 mos old now and his rear is gaining more buoyancy but it will never be as good as many "water dogs". All of my dogs stay on the lean side, with lots of muscling, all their lives so they have more mass per surface area than many family pets who have less muscling and more fat. BTW.... I have been a "fish" all my life and spent years swimming competitively and long distance swimming. My feet and legs
do not float. For years, I had very little lean body fat. When my feet sank and I would then shoot down like an arrow. Now that I have a bit

more body fat it take longer for my head to go under. While on this subject, Jake Mastiff has been able to touch the bottom of the shallow end since he was about 5 or 6 mos old. He does like to walk around on his back feet a lot while paddling with front. This would probably tear a liner. But not many dogs, even when mature, will be nearly as big as a Mastiff puppy. He's 11 mos old now and 30" at the shoulder.
One of my doodles likes to challenge the sweep hoses by swimming over and over them especially when they are on. He doesn't try to bite them though. For first couple of months I always took any sweep out. Now, I don't always but do turn them off with hose pulled to the deep end most of time. They do fine with the Polaris hose (pressure) and the Tracker (vacuum) but my best swimmer, the one who loves to challenge the hoses has gotten tangled in the cord to the Vero (like Aquabot robot).
They now have access to the back (pool yard) when someone is home to keep an eye on them. We will probably always have to be concerned with them leaping on each other, especially the doodles.
A major thing to keep in mind is that when one dog comes out of the pool another dog or dogs, on the edge will bite at them. I don't know why they this but it has always happened. We started correcting them early on. They still do it somewhat but not as aggressively as they would if we hadn't corrected them early with occasion reminders still.
As far as tearing the liner. Once they know to not get out of the pool anywhere but the steps/bench there will only be a few reasons why they would do it and maybe tearing the liner. One would be in a panic situation. The other would be if you used a floating toy that they had to push up the side to be able to get it in their mouths. We have one ball they love but it is pretty large for the doodles' mouths. They have to push it against the side to get it in their mouths. Jake Mastiff has no desire to retrieve. Some dogs just don't so if you want them to you have to teach them.
The doodles drop toys into the pool and then wait for the other one to come and then they leap into the pool together or one at a time, sometimes on top of the other. They like to challenge each other while coming in to steps and sometimes get to steps with a part of toy in each mouth. A good toy for team retrieving is the floating Kong. One can have the Kong while the other holds on to the rope.
We had one Mastiff who had to rescue any person who got in the pool. He would swim circles around you until you grabbed his scruff. Then he would take you to the steps and stay there until you got out. Just like a Newfie. We had to put him up when we wanted to float or play in the pool without being rescued. One of his half sisters never got in her owners' pool unless children were in the pool and did the circle thing until the children were made to get out.
My dogs have "rescued" and "killed" a lot of sweeps over the years because, until these new puppies, they had unlimited access to the back, pool yard. This can be dangerous for
unseasoned, immature dogs, or old, blind, physically challenged dogs or those who just won't leave the sweeps alone. It also gets expensive replacing sweeps and parts. We started very early letting the puppies know what is "off-limit". We have to occasionally give them reminders but they have a pretty good idea that the sweeps and 2 Pool Skims are not toys. They just can't resist the spray from the Polaris tail, though. Occasionally they will get the sponge when they are biting at the spray but they haven't pulled the whole sweep out as the dogs in the past did.
Check out physical swimming capabilities of your particular breed or mix. There are certain breeds that just don't do well in water. You can get life jackets to fit most dogs. If I was going to be boating with my dogs I would probably put vests on them if the body of water was large enough. In any boating situation I would put a vest on my Mastiffs as they don't have a lot of endurance and have to work a lot harder to stay afloat.
Some dogs like to jump in and then swim very close to you. My daughter's lab was that way. You had to be very careful swimming with here to avoid painful, deep scratches. She was such a pool retrieving freak we had to be careful to not throw a toy too close to an edge. She would take a running leap and make it all the way across the pool before hitting the water. On more than one occasion she chipped her teeth hitting the edge of the pool.
There's much more..... but gotta run.
A couple more things. We like the idea of all the dogs knowing were to get out even if they aren't going to be regular swimmers. You will have to reacquaint them to the process every once in a while. We've had more than one "non swimmers" fall in, a couple slipped on ice on the decking. A couple have been visiting dogs who didn't know pools. Another thing is that once they know about steps you can take them to friends' pools and just show them where the get out areas are. Usually showing them once does it. Another issue is dogs who are too pool crazy, sometimes tearing up doors and woodwork, even glass trying to get to the pool. Theses dogs can be taught when it is appropriate or not to get in the pool. The Dog Whisperer, Caesar had one like that on one episode.
[EDIT] All three of my puppies developed ear infections this fall. Only one was showing evidence by shaking his head. They have been on prescription ear drops after seeing the Vet. Two are still on antibiotics. Jake, Mastiff's has totally cleared but still on the drops until we get the drying gel and the Doodles are almost cleared but still being treated. Floppy eared dogs are very prone to ear infections anyway, especially if you don't keep the ear canal dry. Vet says that he will give us an appropriate,
non stinging drying gel to use once they are all totally well. I have the drying powder but Vet says it is too harsh and doesn't work as well as the gel. He said I would need to use it after they swim but they are in and out for hours at a time so I'm going to use the get twice a day on each, mid day and night time, when they won't be swimming till next morning. [end edit]
gg=alice