Ouch. Yeah, I'd go with note. Go to Google, language tools, or ask at the library, clinic etc. A LOT of places have bilingual staff nowadays.
Even better would be if it was from more than one neighbor, not just focusing on you. Since they've already hurt you once, why try and bring their wrath if something does happen to their roo... IE if hit by a car, killed by a dog/cat/coon/possum/fox/etc they may immediately think of you and your 'threat'
Better to make it a community note, perhaps just warning of the dangers of cars, loose dogs, list of other local predators, not to mention the animal control people... with a "Just a head's up from your friendly neighbors' kind of tone... and perhaps an apology for not saying anything sooner... due to the language gap? Maybe throw in the offer to help secure their property using THEIR supplies. Have any who agree with what it says (in English AND Spanish) sign it, date it, make copies for each person who signed it and that neighbor (never know when you might need it) and then send it through the post, with delivery receipt.... and save the receipt.
That way, should anything happen you and all your neighbors can prove conclusively that you did everything you could to prevent a disaster.
Could even make it VERY vague and just mention ALL pets/animals, not specifically chickens. Dogs have been hurt by sticking their nose in another dog's yard before, as have cat's... not to mention the risk of meeting Pepe Le Pew... eww. Do it in English and Spanish and tack one on every door. Hmm... yeah, then no one can say they were 'targeted' but they also can't say they weren't informed of the risks of letting their 'pets' run free in this particular area... not that it's your job to tell them, just a nice thing to do.
Before we moved we had a neighbor with chickens... or at least with a rooster, since the guy would come down to our house and crow day and night. Code enforcement didn't do doodly, since they have X DAYS to respond to calls of loose animals... and too many reports to respond to. *sigh*
Fence wise... from one direction it may mean flying over five fences... but our house for instance... if our neighbor five houses down had a roo, he'd just have to get over his fence, then strut down the 4 front yards between us, and then pop over my fence... two fences total... not near as much effort... still, I'd vote for clipping if you can catch him, and dinner if he actually makes it into your yard. People who let their pets wander like that really don't care all that much, and quite possibly wouldn't have any way of proving that ANY pet was actually theirs... ie papers, pictures, tags as those things are so much trouble.
