If the law around your area is like ours then the police can use the images in court provided you gave fair warning that there was video surveillance. Fair warning here is obviously visible cameras or signs. Maybe worth asking them.
Here in Fla. you don't have to give fair warning of video. Why would you warn them? Warnings only keep honest people honest. Warnings will only help them defeat the cameras. You do have to warn if your recording audio inside a building.
I had a problem with coward kids throwing rocks through an open garage door in my shop. I installed an 8 camera system with three of them mounted looking out that door from different angles. I mounted them low so I could get straight on images. Didn't take long before I got him on video. Worth every dime to see the 14 year old tough guy handcuffed in the back of a cop car crying.
I would use the game camera. However I would use more than one. At least two and maybe three. One mounted under the boat might give you a look at a their car or a tattoo on their leg. Maybe mount one on the inside of the drop in board looking back at the ****. Maybe you could make some sort of canvas bag to cover the masthead that held a camera so it wasn't easily visible.
