GSDs

I'd maybe consider some of the eastern lines.  All lines have enough health problems as it is, I would not be encouraging breeding overly large dogs but there are some lines that just have more "presence".  Some of the eastern (DDR & Czech) working lines have these massive heads.  The dogs themselves are not larger but they look like a dump truck.  Plus a working line is most commonly going to be a darker sable, black, or have more black coverage.  They just look more imposing.  They also sometimes mature a bit slower in the head and show more suspicion in general.  Many work more in defense than in prey so they are more naturally protective and react to threat.  That said though, my Nikon is quite dark with a black mask and also works more in defense than prey.  Depending on how he matures I may do Personal Protection work with him in the future.  Some of the German show lines have big heads and darker masks.

The important thing is to find a breeder that knows what they are doing and can get your dad what he needs/wants.  Litters can run the gamut as far as temperament.  Just today at training we were working some puppies.  The puppy I had (the one that I had in my home for a few weeks before Christmas) came in with confidence, barked well, and bite/struck hard and full.  Later on her littermate sister came in and was terrified of everyone.  Like I said Nikon works mostly in defense but he has a littermate sister that works in prey and is super object oriented while he is not the least bit interested in tugging, winning, or possessing a sleeve (he just wants to neutralize the threat).

Both working lines (any type) and German Show line dogs can be highly active.  Again it would totally depend on the lines and the specific breeding.  Again another reason to find a good breeder that knows their dogs and what they are producing.