Recently we have had some Jacks coming in and crushing schools of mullet on the same flats we are catching monster bull reds.  Although these creatures are fast moving and only give you a small window to get a shot on them if you put the fly in the right place and move it fast enough you can sometimes get a bite.  The key is to get the fly moving fast enough.  Sometimes you have to actually sweep the rod so the fly is moving fast and steady.  This makes it hard to get a good strip set on them but usually when they take it they turn and run, so after the initial run you can usually dig the hook into them.  Here is one of the bigger ones we have caught going about 28 lbs.