I've never had any problems with the dog and the vinyl liner. My dog is a Chesapeake Bay Retriever (about 74 pounds) and she swims in it more than anyone else!
If you want the dog to use the pool, make sure you get one with built-in steps - like I said, my dog can't get out by herself. Anything I get now will either be A. Expensive or B. Unsightly or awkward. I've taught her to rest while standing in the shallow end, but if she somehow got into the pool without us around, there's a serious chance she would drown. She will swim for hours upon hours - which, as you can imagine, leads to exhaustion.
I also bought the Skamper Ramp - it was way too flimsy for my dog, even though I bought the extension for larger dogs. It would probably work with the smaller dogs, though. I keep it in the pool to save small animals that fall in the pool. I'm pretty sure it works because before having the Skamper Ramp, I used to find dead squirrels, rabbits, snakes, etc. fairly often, but none since I got it. It is definitely NOT for medium to larger dogs - maybe in an emergency.
Any other thoughts on makeshift steps or ramps for the dogs?
Thanks