Our dog park was designed by someone that doesn't use them, and maybe doesn't even have a dog. Probably a cat person. Not that that's bad but they shouldn't be put in charge of the dog park.
I have a big orange backpack that I cart a gallon of water and a water bucket in when we go since there are no water dishes and no water source.
Anyway, I designed a water dish that hangs on the fence out of a gallon milk jug that I can leave at the park for everyone to use.
To make one you will need:
a plastic gallon jug
a pair of scissors
Step 1: Cut away the front and sides to make the bowl
I think I will cut the next one so it dips down a little more in the front. It hangs at an angle so the water level is lower in the front than in the back. That will leave more room for the bigger dog's heads and keep the front edge from digging into their necks without cutting down much on the volume of water.
This one works fine though.