Well, in case anyone's still reading this thread... I finally got out and used my 250lb retrieval magnet!! Because of the particular bar magnet having two magnets surrounding by heavy metal casing, I had to first rustproof my magnet.
I was thinking that some sort of Rustoleum spray paint might do the trick, but then realized that the abrasiveness of the sand and metal objects grabbing onto it might scratch the paint right off.
So my next idea which ended up working WAY better than I had imagined was to get a can of that rubber/synthetic dip stuff that you would normally use on the handles of pliers, screwdrivers, or other tools. I remembered seeing some at Home Depot once so I went and got some.
I did one full dip in a aluminum pan, then hung it by a biner clip from a rope between two trees. After it dried, I dipped the steel screw ring on the top in next. I then had to let that dry and followed it up with touch up painting on all the spots that I could find that wasn't fully covered. It took a total of about 3 full days for the setting of the stuff and re-applying process. At first I was sort of "in doubt" about elasticity of the rubber and thought that the first light coating would surely just get ripped off by the metal objects from the water. But after I took the thin sheet of rubber from the bottom of the aluminum pan and tried to rip it, I couldn't get it to do much more than stretch for me. With my 25ft rope, I knew it was gonna work well!
My spot I had wanted to use it on was the 1,000ft pier at Fort deSoto park here in Florida. If anyone's ever watched the newer movie, The Punisher; it's the same pier that the Punisher's wife and boy was run over by the bad guy's truck!!
So anyway, my first mistake was made by going out on Memorial Day weekend.

I only had about two or three 10ft spots to drag my magnet around a bit. I got everything from fishing hooks, to bottle caps, to misc pieces of metal, to even a wooden knife handle with the blade either broken off or rusted off. Those were my finds for the night. I intend on going back out sometime this week again if I'm able. Hopefully there will be less people next time around. I haven't yet taken pic's of my finds, but I'll get them up as soon as I can!
Bran <><