Apollo loves his kiddy pool too. I went out of my way to find a 5ft pool, most are 4ft, and he LOVES it in the summer. Infact he'll usually dunk himself in the pool after being in the mud, so cleanup's not nearly as bad.
Everyone comments on how lean Apollo is, including the vets, so definetly not pudgy here. On the other hand he's put on 10lbs (he was 95lbs mid January) just since we got Arty and I'm reasonably certian its mostly muscle as Arty keeps Apollo running every chance he gets.
You want to be able to tell where his ribs are when you run your hands down his sides, but not actually be able to slot your fingers in between them, so if you can't tell where his ribs are then yah he could probly stand to loose some weight. Keep in mind that all dogs are different too, so the weight thats perfect on Apollo might not be perfect on Lambeau.