We have used them on occasion, mainly for my son, but I also used some at a Hannah Montana concert I recently took my daughter too, and I was still able to hear everything, it just wasn't as intense. No "concert ears" here!!
I can't remember the brand names, but one pair we really liked were a soft, pliable silicone rubber type that is moldable. It fits to your personal shape of your ear and is actually very comfortable. The other pair we like were more of a sponge rubber and they were OK....the insertion was a little awkward because you had to squish it down, then insert it, then let it release and it would fit in, but it always felt a little out of my control, hard to explain.
My son's favorite way of drowning out really loud sounds is actually something your father might like. We have a pair of Sony noise canceling headphones. They're fairly small, have a nice cushion on them, and we hooked them up to an MP3 player and my son uses that whenever we are out in places where the crowd volume will be higher than what he can tolerate.
Maybe you could get an Ipod or MP3 player, download some of your father's favorite music, then get a pair of Sony or Bose headphones. They fold up so small, they really are not cumbersome at all.
Just a thought, HTH,
~Dawn