Why won't my dogs go out anymore?

Well I have these 2 pretty big dogs. 1. Is Diesel an 80 pound, 2 year old boxer/mastiff mix. 2. Is Bear a 90 pound, 1 year old rottweiler/german shepherd mix. Both dogs used to love to run around our backyard for hours and we used to have to chase them in sometimes when they chose to play than listen. Now though both show no interest in the backyard whatsoever and if I do get them out the door they walk out and right back in. Both dogs were fully house broken and now since they will not go out we have had "accidents" in the house. Sadly my father ped away last month and they seem to of started this behavior about that time so I wonder if it is linked. They both did love my dad, So could it be some type of doggy depression?