OK, I was talking about your suggestion of owning multiple large security dogs, not one or two smaller pet dogs.
One can still own a nice "doggy-dog" for companionship and love without needing a team of Dobermans or Rottweilers just to keep you safe.
Policing the yard twice a day? Would you fit that in before or after their twice daily walks?
As far as being expensive goes, a couple of large, trained attack dogs aren't exactly cheap either. Especially the astronomical vet bills.
As I said before, reinforced door frames, high impact windows OR security bars over the windows, adequate lighting and surveillance cameras, don't require any additional work, maintenance, cleaning up after or expense after the initial installation and they don't suffer deterioration from old age after ten or twelve years like animals do.