Around here, most people use Slime for the occasional mesquite thorn. I use it in the mower tires, but it certainly has its limits.
Don't know if they'd be tough enough for the swamp. But it looks like tires-n-such has taken over the Essex line of kevlar belted, run flat sidewall mud tread 6 ply tires. They're not cheap though. But they're made to hold up a heavy UTV, even when flat.
After that, it's probably going to be the expensive, solid tires.