damn man, I'm running out of non-lethal ideas here.. these ppl piss me off, and you're like, 900+ miles from here. start being as obnoxious as possible.. like blasting that "Somebody's Watching Me" song from the Geico commericials

I still vote on fish and dairy products left out in the open... or you can take a trash can and put a bag full of garbage in it - preferably with meat in it - and just let it sit for months on end. let rain water fill up in it and become stagnent.. then finally, take it up to the road but "accidentally" let it fall over and run all that stench into their yard

when I was younger.. like 12 or so.. we had our trash cans out back next to our deck thing (we had no pool, so it technically wasnt a deck), and someone shoved too many bags into one of the cans and it was too heavy for me to move it, so it just sat and sat for probably close to 2 yrs. one day, I accidentally knock the lid off, breaking the seal that kept the smell in, and it was so awful that I instantly threw up.. and it stunk out the house for 2 days. we had to go next door to our neighbor's house, it was so bad

Rip their fence down and with your new found wood extend your deck straight into their kitchen.

loud music is the only thing you can really get away with really or random parties at your house. That sounds like your best bet. Messing up their yard if you want to try something a little gutsy. Thats my suggestions :]

I dont know what to suggest that you do at this point but if you arent willing to take some risks and are just going to keep letting the neighbors have the upper hand then there isnt a whole lot of options.