Subject: I'm trying to set an alarm off when someone takes a bouy out of the water

I work with wildlife divisions across the US and one of my customers is 
having people steal fish from a net that they set up to do studies.  I've 
tried to make a device that will trigger my equipment (a normally open or 
closed state) when the bouy they use to find the net is removed from the 
water (fresh water).  I've tried to make something using 2 contacts but am 
concerned about corrosion.  I've also thought of using some kind of 
trigger using a ping pong ball as a float.  I'm open to any suggestions 
you may have.  Thank you.

Re: I'm trying to set an alarm off when someone takes a bouy out of the water