Shouldn't be, unless someone used seam sealer where the fenders overlap the rocker panel. Are you sure you've gotten all the fasteners off? Front fender: three bolts through the A-post into the back of the fender, three spire bolts along the bottom of the dogleg, four folts at the front (on my TR4A there was also a sheet metal screw), and a number of big spire screws along the top edge.
Rear fender: three spire bolts along the rear to join to the valence, one spire bolt at the front into the rocker, three bolts in the wheel well forward into the B-post, and a number of spire bolts along the top edge.