If you're heading north up to Tenderfoot, the big rock is located about 300 yards south of the actual river mouth. It is NOT in the center, it's on your right (starboard) side. If you line yourself up with the center of the river entrance and stay left of center, you'll be fine. DO NOT veer right of center at all.
Until October, the rock is marked with a jug and along with that, 2 jugs to mark the entrance to what I call the Pile. Its basically a wall of rocks that are about 2-300 yards south of the big rock. Your depth will go from 6ft to 2ft in a heartbeat.
Play it safe, when you get to an opening in the weeds about 1/4 mile from the river mouth, trim up and no wake up the river until you can gauge where the hazards are.
I've owned a home up there for 16 years now and if I had a nickel for every prop/lower unit I've seen destroyed by the rocks and big rock, you know the rest.