Eh, if the landowner would like to see preservation work done free of charge....
It'd have to be in the coldest winter months of the year for safety snake wise, (not saying much in that part of the country), with a lot of snake away thrown out the day before just in case. I know I've killed a lot of water moccasins with a shovel, but armed guards, and or folks with revolvers loaded with snake shot would handle that issue.
Looking at the pictures, and satellite images of the fort, bare minimum on heavy equipment would be two back hoes. Getting them out there could be done with a rented barge. Bare minimum on people working would probably be around 20 people, and also for safety no one wondering off alone. It could conceivably be done over the course of 3 or 4 years, working weekends in the winter, or even two weeks a year. Come summer rain and other coastal happening would probably help clear the fort after the ground's been turned up, but in that case supports would need to be placed everywhere around the fort, especially where digging has taken place.
Another big safety concern would be all the unexploded ordnance, but experts could be had if they're allowed to take them home. Be a LOT of folks lining up to help then.
As for other happenings climate and weather wise, some scientist friends of mine have been expecting a big cool down in the Earth due to volcanic eruptions, solar activity, ice core data, and so on, and I got to say they've been on point so far. Such changes could provided a winter good enough down yonder to help cleanse the place of water moccasins in the next two or three years.
Paying for it? Online fundraiser, plus making sure your volunteers have their own equipment. Owners of back hoes could write it off on taxes for charity.