Inextricably does actually work in the context, but I agree that inexorably is probably the one he meant.
It's still a pretty cool story though, and good on him for figuring it out. On the surface (see what I did there?) it seems weird that the Parks Service wouldn't let him attach GPS blobs to the rocks on the proviso he did it without disturbing the rocks ... which I assume would be fairly easy? Blob on a splotch of epoxy, drop a GPS unit into blob, job done?) After all, they do allow the equivalent onto live animals.