I invented something at the dog park the other day.
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

First, cut a big hole in the front with a pair of scissors,at least half way down, all the way up to the spout and out through most of the sides so the dogs can get their big heads in there.
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.

Step 2: Slice the Handle to Make a Secure Hanger

Slice the handle 1/2 the way down. Don't cut a piece of the handle off, just slice through it and pull the pieces away from each other to slip it onto the fence. It will usually keep the dish from being knocked off. You can't see the slice in the photo but it's there and you can see the handle is left whole, it really makes a difference in keeping the bowl on the fence.
I've started carring a cheap pair of scissors in my pack so I can cut the jugs that people throw away into bowls. It just takes a few minutes and they can be hung at different heights for different sized dogs.