Sounds like your Dad is committed to beating the incontinence so remember the sheath is an aid to recovery not a substitute.
On the coloplast site I answered the survey and because I said I had NOT used a sheath before all I got was the cardboard measure guide and a letter saying they would follow up with a phone call. I got my sheaths and bags on prescription through our local incontinence service, they issue the “Bard Spirit” sheath, same principle as the “conveen”. http://www.bardmedical.co.uk/Page.aspx?id=1455
Like others no problems with them falling off, quite the opposite, can sometimes be difficult to remove, but well worth the effort ,I got a medical adhesive release spray with the sheaths, but make sure the spray is removed from the penis before fitting a new sheath. The incontinence nurse told me to replace the sheath after 24 hours and the bag after one week.
I would wear one when going out and leave it off if I was at home or not going too far. I wore one at night but would still get up if I felt the urge to urinate, this was for two reasons. One reason was because I only had 500 ml bags, but mainly to maintain the routine of urinating normally and I was still measuring my flow rate. I wore pyjama bottoms at night to keep the bag etc all together. During the day I also used a catheter leg/ thigh strap for additional support, a three mile walk with the dog and kicking a ball and the bag stopped in place.
I would have a small leak almost every hour, on one occasion I was concentrating on a puzzle for three and a half hours without a leak, so trying to put the problem to the back of your mind may help. A surgeon also asked me “ do you think about it all the time, try to forget about it”?
As regards the pads slipping is he wearing elasticated underwear, tight enough to keep things in place but not too tight, I use Tenna2 pants which have an adhesive strip to hold them to your underwear.