Look up the elements for criminal trespass in your state. Start with the elements and determine what it will take to prosecute by satisfying all of these elements against an offender.
Make sure the property is properly posted. Document this with dated photographs.
Find out what the procedure is for you to swear out a criminal complaint against offenders, when a situation arises where you can meet all of the elements against an offender. This way you won't have to rely on law enforcement if they are not available.
Finally, if there are individuals that you already know and can identify as being a problem, send them registered mail now with a letter stating that they are not allowed on the property. Given an adequate description of the property in question and keep a copy for your records, along with the delivery receipt. This will help with any question of notice.
Also, consider a civil suit for trespass in order to obtain compensation for interference with the quiet enjoyment of your property.
I was able to successfully prosecute based in part on trail cam photos. It takes a lot of leg work but is definitely worth the effort...successful proescutions are a huge deterrent.
