Now i could be wrong, but this is what i would think of doing. (That is, if sem-fixed is allowed) Bear in mind, that i dont use/have the need to use silt rigs at present, but i do understand the mechanics. This is just something i thought of due to your problem. Still learning myself, but one must use a little ingenuity at times eh?
Maybe you could use some form of break away link at the bottom of the silt rig, so that it snaps off in the event of a snag.
Instead of tieing a lead to the set up (creating a fixed lead set-up) tie a break away link, then attach the lead. (doesn't this then become a semi-fixed silt rig?)
If the silt is deep, you may end up losing a few leads everytime you wind the rod in, but thats only a few pennies right? Isnt catching the fish more important?
Someone please correct me if i am wrong about substituting the fixed lead for a break away link.
Gordon will correct me, i'm sure of it.
^ Nothing to see here. ^