What sort of dogs do you have, have you tried letting them swim to see if there is an issue? I suspect the only time they are likely to scratch is if they panic or get too excited. As you can see in the photos I have a fairly large dog even though he was the runt from his litter (120 pounds), and the only problem we have with him and the pool is if he wants to get out in a hurry and jumps out the side of the shallow end then has to try to climb with his hind legs, even then he has yet to tear the vinyl. I must admit though with a new liner I would probably be more worried as it is mine is getting closer to time to change the liner which is now 12 years old, of course the dog is now 8 also.
Ike