I still think a total station is a good bet.
If it is too thick for total station work it is going to be too thick for GPS.
Maybe hire a surveyor to come along on a days work and help develop a scheme.
@mathteacher Thanks for the reply. Our protocol is actually based on the above link, with some modifications / simplifications for our purposes. Laying the tapes usually takes somewhere between 1 to 2 hours depending on vegetation thickness. The locations are very remote, so we are looking to maximise the number of sampled locations in a day.
Overthinking things is always a problem. Crews always want to think the latest tool will make things faster.
Truly, a good crew with machetes (or your preferred tool) and the cheapest total station you can find will do everything you need to do. Get a data collector, writing this stuff down and then hand inputting it will take longer than measuring it once the line is cut. 25 meters should take about an hour or so with three guys. Everyone starts cutting a line, 30 minutes later (if you cant cut 80 feet of line in half an hour, you cant be a surveyor), then two of the guys start measuring, the third guy can keep up with them since half the line is cut. The data is in, no pain, just a little sweat.