I anchored a 38' sailboat in the last creek before going out to Hawk channel. It's a tight squeeze, I was up against the mangroves in windshifts. The channel going out is very narrow and has a bend but was well marked. I went out at night with a spotlight, suggest you have a spare spotlight ready in case the other one fails. I never heard of the rock. 

Bill

I have cruised the Intracoastal from Melbourne to Marathon and up the west coast to St Petersburgh many times.  As for Anlefish creek I never had an encounter with the rock at the Hawk channel end but my draft is only 4 feet. You can anchor in the creek but don't venture up the side channels, and ues good ground tackel.  The current will dominate which means you will do a 180 degree switch with the change of the tide so use two anchors. I have also anchored in tarpon basin. I found that there is a good area off  the south west shore.  Beware of the shol in the middle of the basin, but if you need less than 5 feet you can get around the shol via the south west approach. 
Richard A Bruning

Subject: Andelfish Creek
Cruising News: We entered the channel from Card Sound at mid tide and we had 7 ft. all the way to the anchorage at Middle Creek. We had 9-10 ft. in the anchorage. It was a great spot in the mangroves. We left at high tide Hawk Channel side to 7-8 ft. We did not find the elusive rock.
George & Carol Myers
S/V Traumerei