I'm fortunate to live on the site of my two ponds so I don't have the trespassing problems seen by others. A number of options have been discussed in this thread and others. For all you absentee owners, would it be possible to find a responsible "local" to police your property in exchange for fishing/hunting/trapping/recreational priviledges? Of course, this could open the door to liability issues which, unfortunately, are a concern for all property owners, especially in todays climate to sue first.
Sunil, I think Clearwell's flower display is an attempt to instill in a trespasser's mind that this is where he/she may end up if caught. In addition to the flowers, get yourself one of those science classroom skeletons and position it by the pond with a sign stating your dislike for trespassers.
Russ