Getting a bit more serious, developers along the Space Coast clear lots of palmetto for new housing. Their "normal" attack is D-8 (or larger) Caterpiller with a three-shank ripper. That goes deep enough to get all the roots, but even then small bits will re-root and sprout -- but at that size, Round-up will kill em. Most of the stuff on my property had lateral root-trunks that were 4-6" in diameter. There probably is a quantity and concentration of Round-up that would kill those, but I couldn't afford it. I had pretty good success working it very slowly with the bush hog and then clearing the chunks with a landscape rake. Ended up moving a lot of dirt around, but I couldn't find anything else that worked. BTW I had some that had its roots intertwined in live oak roots (and I didn't want to kill the oaks!) so it just kept coming back.
VistanTN
ex-VistanFL