Swamp, I don't doubt that. It was probably more my fault that the keels popped out.
I know one keel came out on it's own, but I think the others came out because of how we put them up. We normally drag the boat out with us after the hunt and drop the anchor just enough that it will stay put. We then pick up the decoys, wrap up the line and chunk them into the boat. That could be anywhere from 2' to 20'. We definitely don't baby them.
The silicone worked out great. I didn't have a hot glue gun and wasn't going to buy one just for decoys, so I used the silicone. I have tried smacking the keels on the hearth and I can't get the keels out.