Making a combination slide bolt

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It's certainly sturdy, but with only 3 digits in the combination it couldn't really be called strong. A slide bolt like that would be on the inside, though, so an outside attacker wouldn't be able to access the dials until they go over the fence, however at that point it may well be simpler to just unscrew the device from the gate. 

It may be good enough, though. Mostly it's going to slow people trying to take heavy objects (ones that can't go over the fence the same way the people got in) off your property. No lock is undefeatable but if it slows them down enough that may just provide enough time for police to arrive, or it may simply demonstrate that your property isn't the easy pickings they thought it was and convince them to try some place else.

Build Your Own Porch Pirate Package Protector

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Now you too can defeat porch pirates with magic. Not Harry Potter magic, mind you, more like David Copperfield. Practical stage magic.

Laser cut wooden combination lock

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There's nothing quite like building something with your own hands to gain a better appreciation for how it works. Watching someone else build it is pretty good too, but not quite the same.

Fourth time's the charm

from here (image source)

Locking your car like you would your gate doesn't seem like it would be very effective, and it looks like the holes bear that out.