What do you think?
Get yourself a flipover shack - easy to set up, easy to tear down. Nobody sees you pulling in fish, nobody joins you. (My Dad has 2 Frabill Ranger Solo's for sale.)
From your description, sounds possibly like there are cribs in those spots?
Several lakes around Eau Claire have cribs and people have them marked on GPS - each year it's a race to set their permanents down right over them, then they "own" that spot until shacks have to come off.
Not right, but not illegal.
Next time, if the action is too fast to use 3 lines, put an unbaited line down the other 2 holes.
One other thing I've noticed is there are at least a few people who have seen the different cars in our group and have followed us to more than a few places. Places we'd never seen another soul. Places that everyone thinks suck and have a one star rating or no reports on LL. Heck even places the DNR and LL don't know exist. They've followed us. SE WI is a tough place to fish. Lots of fisherman but even more followers. Six months until I'm done with school and I'll be running to northern Ontario or The Dakotas. 7 months of ice fishing baby!
Also if he was within 5-10 feet call the warden. That's harassment of a fisherman. At least in WI. Just went over this a week ago with the warden. There's no set distance it's the wardens discretion, but I'd say 5 feet most wardens would issue a ticket. At least I'd hope so.