So the little things a kid might do to startle a regular dog isn't going to phase ours at all." Mr Grennan, a former boxer, formed the company 10 years ago with just two dogs after suffering a hand injury that ended his career.
They now own scores of dogs, many that live in the house with the family on a 150-acre ranch in New Hampshire, USA.
Mr Grennan, 28, said: "A dog the size of the Hulk could kill someone if it was in the wrong situation at the wrong time. If he bit down on someone's arm with full power it would snap like a toothpick. These dogs are very balanced and gentle - they are nanny dogs." Despite the lethal potential of Hulk and the couple's many other dogs, three-year-old Jordan has grown up with them within arm's reach.
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' We pointed the camera at Piper and he said, 'yep, I am'.
"The captain just looked at us like, 'you guys are nuts'." Improvising the shoot on almost no notice: "I called up Alcatraz the day before, and I said, 'hey everybody, we're real excited to come over and do the video after everybody goes home.
So that's my job, to try to alleviate somebody else's fear by giving them a family dog too." The Big Short, the film adaptation of Michael Lewis' book of the same name about the causes of the financial crisis, opens in UK cinemas this weekend.
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"I have no concerns about any of the dogs around my son," she said. People say these dogs randomly flip out, but that just doesn't happen.
"They go through enormous amounts of training and are more used to going up against multiple grown men and hearing loud noises.
"But I've got clients in Grenada and parts of Africa where there is. They don't don't live in Candyland, they live in fear.
"And why should somebody else live in fear if they don't have to.
Mr Grennan said: "A dog like Hulk can cost you anywhere from ,500 to ,000. You could throw ten million in front of me and I'd throw it right back at you.