Here is a patent on someones snag release feature for an anchor.
Patent US7870831 - Anchor with snag release mechanism - Google Patents
Don't go with this one but be sure you have something that accomplishes the same thing.
What you want is the ability to pull from a different spot on an anchor, near its bottom, on any anchor jammed in-between rocks or ledges.
Take an anchor like this one:
and you can generally get a jammed anchor to release by pulling different directions.
If however, you cannot row upstream ..........
Attach preferably a chain welded or linked to the bottom of your anchor.
Have it of adequate length to loosely reach the top.
Then connect it to the anchor top with a slightly heavy garbage tie.
This is an intended weak link for when things jam up.
Attach your rope from the boat to the chain top. Not the anchor directly.
A double wrap garbage tie will hold under normal use.
You get stuck while downstream pull like you're on a mission.
The garbage tie breaks and you are now pulling the anchor from its bottom in a manner to twist it out.
This is an age old problem and many solutions have been effected over a couple thousand years.
This latter suggestion with the garbage tie is provided for those economically challenged such as myself.
This is similar and shows something of the concept;