when it comes to pure jiu jitsu there is only 1 way to pass the guard and thats to apply pressure wiht your hands on your oponents stomach and to dig your elbow in his theigh and usually he willopen up to do the pain or due to you simply "prying" his legs apart. Of coarse is he is realyl good/tough/been doing it awhile he might be able to withstand this. Of coarse you could reach benind yourself and simply try to pull his legs off you but this is not a technical BJJ move.
So when in doubt wait it out, you guys cant sit still if your inhis guared eh should be looking for guilotene's and triangles and armbars and kimura's etc etc and when he moves aroudn to attempt a move is your chance, especially an armbar or a kimura because he has to "break" his guard to apply these moves. Gulletine is ment to applied with a good guard locked down so dont keep your head down on his chest thats common mistake you want to sit upright while digging your elbws in.