we put a scarecrow out by the pond, and move it every couple of days, the first day it was there, our local heron circled the yard 4 times, then moved on. an old farmers trick is to spray it with cologne, keeps the four legged critters away also. Another deterent we used is tiki torches, with 45 lb test catfish line strung about 6 inches up, and then 24 inches up, surrounding the easy access points of the pond. if he sees it isn't easy to get in, he'll assume getting out of the pond won't be easy, and give up. we haven't seen his ugly hide in about 2 weeks, and hope he stays away!