Mountable grass gator

Just do it. Do it. It's the right thing to do. Let us mount and tame it. 

Have specific places to moor it similar in function to a salt lick, feed it kelp. That's fine. If it eats nothing else but kelp, so be it. Or fish. I don't care.

Even if it can't really go on land, that's fine. It's not a beefalo anyway. Have it function so you hop off the gator when you get too close to land and when it bucks you off, well, the punishment should be straightforward; You die.