I guess my point is if you're bending over backwards to try and find athletic mastiffs you might be inclined to sacrifice in other departments. Like this dog's temperament is not perfect but it's athletic and that's SO hard to find in a mastiff so we'll go with it. Not saying you do that but I could see this sort of thing arising if you're expecting the dogs on both sides to have no weaknesses, you're bound to sacrifice excellence in the main department you're trying to get out of the cross if you're trying too hard to find a balance of good qualities. A dog really only needs ONE quality that's excellent to justify using it in a cross IMO, you just then need to be prepared to test hard and cull hard. People I know if they want a leggy fast bull terrier they don't cross a bullterrier with a slightly faster bullterrier, they cross a bull terrier with a track greyhound, why beat around the bush? Yes the track greyhound is lacking in bull terrier qualities and you'll get a mixed bag of a litter but then over the generations you can select for the bullterrier's good qualities and the greyhounds good qualities and get a nice leggy fast bull terrier, much faster than you ever would have got crossing fast bull terriers, and probably while having to sacrifice on good bull terrier qualities in this desperate search for speed out of bullterriers. Instead choose really good bullterriers and really good greyhounds. Basically it's about playing to the strengths of the dog type you're incorporating into your lines. Mastiffs aren't overly agile with great stamina and athleticism, but they're strong with good protective instincts and so find a strong one with good protective instincts and don't worry so much about their athleticism, then find an extremely athletic bullbreed with endurance to cross it with. I'm just saying that would be my approach and I know is the approach of a lot of people who breed hybrid dogs for performance with undeniably outstanding results. You're aiming for the strengths of a dog type when you use it in a cross, you're aware of it's weaknesses and that's precisely why you're outcrossing to another dog type, to fix that. I just think going out of your way to find an athletic mastiff and rejecting non-athletic ones is the same as going out of your way to find a big protective pitbull to use and rejecting smaller ones. It just shouldn't be the main concern IMO, we know apbts are small and not really guard dogs and we know mastiffs aren't overly athletic, that's the whole reason for the cross. Play to the strengths of the different dog types and somewhere in the litter will be a serious gem with a combination of the outstanding qualities of it's parents. Keep in mind I'm not criticising your dogs at all here as I really don't see a weakness and whatever you're doing appears to be working, I'm just noticing your views and philosophies might differ from other people, people who are also producing great dogs.