First I'd like to thank you for service to the criminal justice system. Good attorneys are IME few and far between.
I think you should take this extremely serious. In my humble opinion... the incidents seem to be esclating. The latest incident with someone on your property. With the information you've given I believe this to have been a probe of your reaction, reaction time, and defense capability. As everyone else suggested I think you should document these incidents with the police. Record any threatening calls. Notify the Judge in the trial part of your ongoing issues.
Tacticaly speaking ... some great suggestions from the members. My tactical advice would be to get a small revolver that you can keep in hand, and hidden, when entering or leaving your home... Carried in addition to your regular autoloader. The advice about the shotgun is priceless IMO. Nothing says "maybe I should reconsider" like the sound of a pump gun being cycled. Being a gun nut I tend to see a firearm as a valid soloution to a lot of problems... But sometimes the option of a firearm is the best soloution
A dog and or a camera are great... but they are easily dealt with by a professional. The whole idea of yhese folks doing reconisance(sp) at your home... That kind of un nerves me.