He won't get prosecuted if the propertys not posted, gun in arms or not. Once he's warned by the land owner, it's the same as being posted. Posting property is necessary if there exists continual trespass. Personally I do not like posting my property. If it's necessary, I will post. Again, the local game law man can and will effectively get the guys mind right if he's not a knucklehead that just wants conflict with landowner and law. Either way, 100% of the time, the issue will resolve one way or the other.