I think the only way to make a hole in trans pan is to be very unfortunate and hit a rocky sharp bump with it as normally the sub-frame and exhaust (as mentioned above) take all the scratching first, then the oil pan and lastly the trans pan ... so your car would be pretty much done before the trans pan got ripped ... unless you were VERY unlucky, just saying
EDIT:
you should go to your GPS navigation/map settings and select Avoidance for non-asphalt/rough roads (or off roads or whatever it's called) ... at least I have that in my Garmin

also set that navigation for fastest routes, not the shortest ones

shortest doesn't mean quickest hehe