A minefield consisting of low-power landmine blanks that detonate without shrapnel a few feet away from the trigger. Weight sensors around each mine blank would ensure that they cannot detonate if anyone is too close. A mine blank works just like blanks fired from guns. A powder charge that looks and sounds like the real thing from a distance of a few feet, but doesn't actually hurt you. Take a step on the lawn, and a landmine detonates a few feet in front of you, leaving a realistic crater and scaring the piss out of anyone who thought the warning signs on the edge of your lawn were a bluff.
Armed/disarmed via remote. Keep them armed at all times, and disarm them via remote when you need to cross or allow invited guests to cross.
You may want to move your mailbox to the edge of the lawn if it's not there already.-- 21 Quest, Apr 06 2009 anything that's gonna lift 10-20 lbs of dirt into the air [edit: and produce a //realistic crater//] is *not* gonna be friendly to anybody standing //a few feet// away.-- FlyingToaster, Apr 06 2009 Not friendly, but not dangerous. It might knock 'em down, but on grass it's a relatively soft landing and that's what they get for ignoring a sign that says "Danger: Minefield!"-- 21 Quest, Apr 06 2009 Spin-off product: armour for JWs, high pressure salespeople and postal workers. Or maybe zorbs.-- nineteenthly, Apr 07 2009 A zorb wouldn't fit through a normal-size gate, and if it did you'd just get blasted back out onto the street like a pinball, and the day you invent effective landmine-resistant body armor will be the day the US military makes you a millionaire.-- 21 Quest, Apr 07 2009 You could bounce over the gate and the minefield if you aimed right.-- nineteenthly, Apr 09 2009 I don't see how this is geared for in-law deterring, specifically. [-]-- daseva, Apr 09 2009 You're gonna probably get in big trouble for this invention...doncha think?-- blissmiss, Apr 09 2009 I prefer my in-laws to my parents sometimes.-- RayfordSteele, Apr 09 2009 Of course the cops would.probably get called the first few times, but I could just deactivate the mines and let the dogs out, and it would appear that they dug the holes. Of course it wouldn't stand up to a forensics investigation, but they probably wouldn't even bother unless someone got hurt. The cops in this town are apathetic on a good day. All I'd have to do is walk over the lawn (with the mine blanks deactivated) and show them some holes my dogs really have dug and they'd be pacified.
(edit) please forgive my typing errors in this anno. It's my first time typing on my new phone, and they keyboard's tough to get used to)-- 21 Quest, Apr 09 2009 The best deterrent for in-laws would be pictures of you doing unspeakable things to their daughter posted on the front door.
But I like the safe landmine idea, wide variety of applications.-- vfrackis, Apr 09 2009 How would the sensors stand up to the weather, and also wouldn't they be able to avoid the mines by not stepping on the patches of fresh lawn, either that or after 6-months, you simply have craters.
Burglars would get an interesting surprise also!-- Skrewloose, Apr 10 2009 random, halfbakery