Aside from bkt's excellent advice gungirlie you may want to look into a Loc-Box Firearm Security System by Mossberg.
This is a wall mounted, key operated device and, if need be, you can keep the magazine loaded, chamber empty, and still have the weapon handy.
Here's a link to the product page...Loc-Box Firearm Security System
They will fit an 870, I already checked that.
BTW, when my "youngin's" were small, the Mrs. and I would unload and lock our pistol every morning, the reverse at night.