First things first. Make sure you clean the coop very well and call the police to make a report. Keep the empty jugs to show the police.
Next thing you have to get defensive. Look up the "posted" land laws in your area and you need to post "No Tresspassing" signs on your land. I know the laws here in NC are that there needs to be a sign at least every 600 yards and at every corner in order for land to be considered posted. Purchase locks, for your gates and coop, you need to make it as inaccessable as possible.
You should really, truly look into purchasing a security camera, you'd actually be surprised how affordable they are. You do not need anything extremely high tech, just something you can point at your coop to catch any perps. You can also post signs or survellance and set up phony cams that blink and attract attention. But, in my opinion, if you are going through that much trouble, you might as well get a true functioning camera that can be invaluable evidence in a case like this.
-Kim