7-C's

I had a cache I intentionally submerged with weights in a water proof box. I tied it to a tree with fishing line and a lure on the end of it so that it looked like a snagged line. The change in water level with the seasons forced to me to archive it but if there is a branch or dock to fasten it to where the change wont effect it that might work for you. It would also be accessible from land and water that way.

I've found weed in several caches which is cool but inappropriate for kids. I stock up on small toys at the dollar store and value village dinosaurs, bugs and snakes, marbles, whatever really. When I place a cache I always leave an unactivated trackable for the FTF and I spend a little more on the swag.