Discussion: Even though it seems sub-moron...

Even though it seems sub-morons would allways be over-estimated, in truth you should never underestimate their sub-moronity. When it comes to destroying things, they have no equals. I reckon no mere steel gate posts are going to do the trick. You will need a Maginot Line occupied by German soldiers in order to even have a chance.

"steel gate posts ..." Any way to electrify them?

You'll never beat them by escalating. Put up steel gate posts, and they'll return with a cutting torch. Put in a concrete wall, and they'll bring dynamite. I think this is going to require a stakeout. Maybe feed them more of the same wooden posts for starters, and monitor the situation, to figure out what day of the week (and time of day) they operate. Then we wait, and ambush them. Rush up and either slash the tires or steal the truck keys. And then force them to do punitive yoga.

...Then leave them out there with the FDFs.

Or take their pictures and report them to the authorities for trespassing...