I agree these occurrences can be explained by other factors, did the wind ball your cord up getting it tangled in the branches around your stand? Its happened to me before. As for the seat cushion, was the hole a clean slash as made by a knife or was it torn open as by claws?
Not trying to go against you here but simply playing devils advocate before you do or say something, look at all the possibilities. If the fact is that someone did mess with your stuff, don't include the landowner since it is not his problem, his property wasn't damaged no need to include him. That being said, is there any way to reconcile with said vandal? Not accusing him of anything but simply taking the higher road? If that can't or won't be done, who is to say what you should do, battle royale???