I wanted to display my milsurp rifles rather than turn them into safe queens, but I also didn't want my kids to have access to them. I had some old hardwood shelves lying around, so I made a nice weekend project out of turning them into a "secure" gun rack.
I realize that any thief with a crowbar or a bolt cutter will make short work of getting the rifles out. But without either of those tools, getting them out will take some doing. Most of the screws (galvanized 4 inch) are hidden from view, and the ones that are visible are intentionally stripped. The slots and holes for the rifles are tightly fit so that the rifles have very little wiggle room.
All my ammunition is locked up in a separate fire-proof safe on the floor.