Heavy without ever hitting the mats with you its hard for me to get a good idea of what you are talking about. Personally i've found that quite often people just panic from the guillotine versus actually being choked from it. The reality is its a pretty hard choke to land. You have to get your forearm under their chin and you need to have them in your guard so that they can't create space. Some pointers are working on where you place your head when you shoot. You want your head on the inside not on the outside of their body when you go for a single or double leg takedown and remeber to keep your chin tucked. In the event that they do get the beginnings of guillotine make sure to not get caught in their guard. Attempt to tuck your chin and turn it into their body to create space. Also attempt to get your body perpendicular to theirs. If your opponent only half way has the choke in they will usually gas after a while from the squeezing. Also there is a great choke you can use that is similar to the python or arm triangle I'll see if I can find a video. If your opponent attempts a standing guillotine(which is stupid) bear hug them and use an inside leg sweep. You must drive your opponent into the mat careful not to end up in their guard(half gurad is fine though). Typically the concussion from your take down will knock the air out of them and release you from their hold. I've had this work spectacularly in competition. If you are simply working on Sub grappling then before you shoot attempt to gain wrist control(this really doesn't work for MMA though) and give a good shove or jerk. It will put your opponent a little off balance or force them to shift their stance giving you the that half second needed for the takedown. I myself seldom use singel and double leg takedowns b/c I'm just not quick enough. I find myself quite often in a bad position when I shoot and miss. I prefer to pull guard or work throws and leg sweeps it lessens my exposure to moves like the guillotine... maybe something you should think about. A much more dangerous move from a failed shoot is the gator roll. Do you know it?