A stable dog hard to tell on the first day or form a computer but things to watch for are does he look away, lick his lips or his eyes start darting when someone bends down to pet him if he does he may be shy possibly leading to a bite. Drop something loud like a pot or pan 10 feet away is he skittish, neutral or comes to check it out skittish is no good but let him get use to the house first. Try him on different surfaces see how he reacts then try something unstable like a box or bridge. When you walk him see how he is with passing dogs there are endless scenarios he might fail at first but will improve with training and trust. One thing I do recommend is playing settle with him you get him to lay down or go to him when he is laying down with some treats and pet him while giving him treats and saying settle after you have done this a few times and he stays put and you trust him get him to lay on his side giving him treats petting him saying settle till he will stay there as long as you want he has now submitted to you can use this to cut his nails take him to the vet and transfer authority to your partner or kids with your direct involvement saying settle they soon lay down without a fuss if you are constant my three year old can do it to my dog now. I sold a rottweiler to friends 15 years ago and when the dog was 9 months old he bite both there kids they always play fought with him but not he was growing up he was taking over I went over and taught him settle I got the 3 & 10 year old to do it the 3 year old would do it all the time looking the near full grown rottie in the eye grabbing his face and rolling him over so she could sit on his head he lived another 9 years they never had a problem again he was a great guard dog. It can be used for dog aggregation also. As far as dogo or presa I don't know dogos have no weight limit males should be 110pd's minimum http://molosserdogs.com/e107_plugins/content/content.php?content.465 presa's do have a weight limit in Spain but not the UK they have a 100pd minimum no max but they both allow the color black http://molosserdogs.com/e107_plugins/content/content.php?content.2821