Southerman13, I am neither an attorney nor an environmental expert. I am merely an old old-dirt appraiser in SE Georgia.
Yours does not sound like a wetlands impact that would be legal under the silviculture (timber growing and harvesting) exemption of the U.S. Army Corps of Engineers. But it might.
You probably know this, but please be patient with me: The Corps of Engineers monitors regulator wetlands and decides on wetland impact requests. But for unauthorized impacts that are not mitigated as required, the Environmental Protection Agency (EPA) prosecutes such actions, and huge fines, as well as prison time, have resulted
Your owner/client should engage an environmental expert whose work has been found acceptable to the Corps of Engineers, and have that expert render the owner/client an opinion as to what work can, and cannot, be undertaken where the fencing is to go. It make take an application to the Corps of Engineers to get permission to operate equipment in the wetlands; at one time, work not involving wheeled or tracked equipment (e.g., manual post hold digging and rolling our fencing by hand) was allowed in the wetlands, but that may have changed.
Please be aware that the wetlands regulations change frequently, (my copy of what I believe to be the latest is 110,000 words, and moderately difficult to read). Also be aware that different Corps districts have different interpretations of what impact regulations are allowed, making it even more important to utilize an environmental expert with recent experience in dealing with the regulatory personnel of the Corps district that has jurisdiction.
Glad you asked, and sorry my non-official response could be no better.
Please keep us posted on whatever happens, including where you found me wrong
Neill (always eager to learn)