I am not too sure of what the law/rules state. So I don’t know what the impeding guidelines are. But, as much as I would like to scream and throw my ice scoop at the guy who I feel is somewhat “intruding” on you; I think the bigger thing to do is to get up and move . Maybe you try that new spot on the lake that you have been wanting to try. I think the clueless person next to you will have a lightbulb turn on in his head when he sees you packing up and then he may realize that he shouldn’t have gotten so close. And who knows, you may find a new spot that is holding some nice fish.
Personally, I don’t know how anyone could justify that in their right mind to come and drill a hole a foot within’ yours. Unreal. I think we should all take a class in sportsman ethics and etiquette.
I hope this helps.