Was this an old clinet that was ticked?
I know that it would be inconvenient to clinets but you may try a buzz lock for the door. You can pick out the recep. that you think most likely to spot "bad eggs" and then put in a call to you to make the decision before they "buzz" in the person.
There are some law offices even here in Eugene that have these. Law firms either make great friends or greater enemies (from what the lawyer at one of these firms here said).
Baseball (or if your country does more cricket) then put those on the wall (so they are easy to get to). To make it look like a "collection", do a few forged signatures of older, dead, players that people would know of. This way, your "weaponary" looks like a harmless collection.
Just ideas, hope something will work for you
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Wayne