I posted this before. Go to Walmart and buy the small self contained motion detector alarm. Runs on a 9v battery all summer and squeals damn loud when someone gets in your boat. Thats all you need to get them to leave. Works with a little keychain remote and is about the size of a handheld gps. Mine is under my helm mounted with double sided tape. The dtector is aimed so it only goes of if you step into the boat. You can take the cover on and off w/o tripping it.