This may be a little off-topic, but, since there are more experienced people here, I think it's right to ask.
Do you think that one can defend (him/her)self from a grappler with Aikido techniques, on the ground? I don't mean the "a successful Aikidoka wouldn't go to the ground in the first place". Let's pretend that you fell to the ground.
Sure.... use a jo, no I am not cheating, jo is very much part of the syllabus.
Failing that... learn how to T3H GR4PPL3 [tm].