Winch security

I have heard of caps that encase the head of the bolt that holds the winch to the bumper. They are steel versions of the yellow or black number plate screw caps. But I can't find them anywhere. Does anyone know what I mean and know the proper name for them and/or have a link to somewhere I can get some please

I just welded a square piece of metal over one of my bolts. They can't get to it then, got the idea from Paul d. However they can just take your bumper off and take the lot.

Sheerbolts?

I'm planning on welding my bumper to my chassis rails so that will stop them taking the whole thing. I have heard of welding a piece of box section over the bolts aswell but was looking for the easier way of doing it with the bolt caps but just can't find them. I'm thinking I'm just not using the correct name to search for them

http://m.ebay.co.uk/itm/25-x-Secure-Nut-Caps-Cover-Caps-M6-M8-M10-M12-/321802585055?nav=SEARCHSEARCH
They are that sort of thing but metal and the cap knocks in flush so the only way to get them out is to chisel the cap back out

That's what I'm looking for. Knew I'd seen them somewhere. They're in the Haynes book showing how to modify a disco