Bridle-less/tack-less & Parelli
Parelli is a good place to start, I do not agree with all of their methods but some of them are great.
I would recommend reading Dancing With Horses and The Horse Seeks Me, its all great information and training for both the horse and rider.
On bridle-less riding and tackless riding. Yes anyone can do it on a well trained horse. But you should be able to do it through trust (In the horse and the horse's trust in you) without or with very little training.
I ride my four year old paint tackless and she has only been ridden a dozen times.
Yes training is great and very useful but you also need the right relationship with the horse.
If your afraid your horse will run off, what does it matter? Its a 1000lbs animal if they want to run off they will do it with tack or without. And there is nothing you can do about it except going with them.
Just my two cents.