Re: Aikido against strong people...
There is always someone just around the corner who is bigger, stronger, meaner and more indestructible than you could possibly imagine. Your aikido technique might work, and maybe running him over with a large truck might work too. But the bottom line is to apply your aikido technique properly and it will likely work with virtually anyone.
You can have some fun playing with the idea if you want. Get a partner who is bigger and stronger and ask him to give you varying levels of resistance. You will find that if you apply the technique well and gain kazushi, you will often succeed in taking him to the mat. It is also a lot of fun to play around with henka waza too. If your partner is able to prevent you from doing Technique A, then you immediately switch to Technique B and see how that works. Both practices can be fun and enlightening, but should be reserved for before or after class. Most sensei would be a little irritated if you were experimenting like this in a regular class. Just remember, NOTHING works every time, but with quality practice and training, aikido usually works.