Paranoid.
I've only been to that zone one time, but here are a few pieces of info in response to your request.
Here is a link to the trip report I put together when I got back.
ColeyG's Belize Trip Report We spent a fair bit of time on Key Caulker and a few days around San Pedro. I was hoping to do a fair bit of walk and wade fishing rather than pay a guide but I found the opportunities pretty limited and uninspiring from the beach. As AP mentioned, the bottom is pretty mucky and grassy in a lot of places and that's makes wading tough. The locals say that bonefish are typically abundant in the area, but I found them few and far between.
After a few days of exploring I found a few "micro flats" on the ferry dock side of Caye Caulker that the bones were using at first and last light. They got pretty spooky during the day in the skinny water.
There are some creeks and smaller lagoons on the side opposite the ferry dock and rumors have it they can hold baby tarpon and snook from time to time. I didn't see any. Don't fish for the big tarpon at the tarpon feeding dock, the locals will burn you at the stake. Canoes and kayaks available for rent at a number of places on the island.
I fished one day with a guide out of Caye Caulker, the company was "Go Fish Belize." Conditions sucked (wind) and I caught one lady fish. I think there are two or three "guide services" based out of Caye Caulker but I get the idea that there are only a few guides to go between a few different booking offices.
I have a bunch more info I could forward via PM if you are interested. I sent some of the stuff to Mingo a while back and I think he could probably add a lot of more useful info as well if he is still around. Mingo?