besides whats been mentioned and necessary regarding a trainer experienced in molosser breeds... other recommendation is redirect that monkey business...which i think would be a good choice to attempt...that is get a toy/toys your dog likes, a soccer ball, tennis ball, frisbee or whatever...something you can kick or throw...and just before you let your dog off lead...chuck the toy, kick the ball & let the dog get focused in on it initially, before the bratty crap even starts...then let it loose off of the lead...have a couple of toys & keep dogs interest/prey drive in those...ignore the bad behavior and redirect with toys & praise the positive...cuz it can backfire sometimes when you acknowledge the bad behavior in any form if your training knowledge is possibly questionable in this circumstance...its still attention the dog has figured out it can get and feed off of that...