Re: I cant take much more
In order to prevent accidents, I suggest a simple anal exercise which is to tighten and release over and over again. This is the same concept as the hold and release exercise for urinary leakage.
The psychological consideration on a previous post is almost on the mark. I think a type of bio-feedback is needed to control the urges. Mentally tell your bowels that they have to hold on for awhile, much the same way to would discipline a child.
I have an aunt that periodically suffers with your problem and I know she has a lot of stress in her life so I am guessing that it's part of the reason for the bowel problems. She has been diagnosed with divirculitis, so that may be a contributor as well. Stress is a wicked thing in that it makes conditions worse. One other thing with her is that she doesn't get to sit on the toilet for very long as she has a demanding autistic and blind adult son--so I am sure that this is one more reason.
So, stress, physiological conditions and letting yourself empty in one visit regardless of the time spent are a few things for you to consider.