Unless you have proof they shot at something on your side of the property line, what does it matter? Did "their" arrow have their name on it? How do you know it was theirs? Is it possible they shot a deer on their side and it shook the arrow on your side?

Wear your orange vest and hunt wherever you want on your property. If it's 1000 feet from the property line or 10 feet, it doesn't matter as long as you are on the correct side of said line, IMO