Instead of just building in Creative with friends I'd rather play a Survival game with them :> It's way more fun that way! Also... Jesus we need fences that are one and a half in block height. It'd be so much easier to capture and breed animals as well as makes more room for creativity.
I already made a topic bout it, "Multiplayer Survival Worlds" Just pointing out if you didn't notice. Anyways, fences seem like a good idea as well, these blocks are hard to see through, I have to come out to see the hundreds of cows and sheep and chicken I've captured. But, fences would be much weaker and monsters could kill the animals.