Hi, @jmy75 !
Did your dad have a low anterior resection? Did he have radiation for rectal cancer?
Both of those procedures can affect the internal sphincter and make patients prone to fecal incontinence. There are solutions for it, depending on the gravity, the overall health of the patient, their age, etc. Your dad may be open to having pelvic floor therapy which is quite helpful in controlling fecal incontinence. The best kind of PFT includes biofeedback and neurostimulation. They may add PTNS (percutaneous neurostimulation of the posterior tibial nerve), which acts on the sacral plexus. Also PFT teaches you to breathe in the correct way for your pelvic floor.
There is also an implant that can be surgically placed to help control fecal incontenence. There has to be a careful analysis and a trial period, to make sure the patient is a good candidate for that solution.

I work as a translator and spend a lot of time seated. I use an ergonomic mesh chair. But the chair alone won't make enough difference to avoid accidents, I think.