Wait for El Creepo to start sucking your wheel. Pull out your cellphone and call police non-emergency dispatch (or, make a "pretend" call if you don't want to actually call someone). Then in a very loud voice that he can hear describe how there is this really creepy guy following you too closely on the Samm bike path and start describing him and your location on the trail. Maybe even slow down and glance back at him a few times while describing his build/height/stats and what he's wearing and what he's riding.
Yeah, that oughta do it.
