L.T. was known to lighten up a room with his personality, and it sounds as though his dog did pretty much the same thing. The above photo is them enjoying a moment of relaxation.
Dogs and humans have been depending on each other (or 'peacefully coexisting' as in 'fish', according to George W Bush) since prehistory. There are pre-historic roads that lead between the North and the South of Britain, flattened smooth by drovers who used big, indigenous dogs to keep cattle under control before the days of the refrigerated transport of dead meat.
These dogs would often accompany the drover south to north, or vice versa, then make their own way home without the cattle or their master - often a distance of many miles, and they were trained to stop at the very same Inns as the drovers, who had left money with the Landlords for their food and bedding for the night. The Landlords or Ostlers would feed them the next morning, then send them on their way, often to another Inn 30 miles away, where they would be given the same board and lodging until they arrived back at their home farm - sometimes involving a journey of many stops over several hundred miles.
Small, stray dogs in towns and cities would - right up until the end of the 19th century - arrive at coaching inns expecting to work for their evening meal. They would be placed in a small treadmill by the side of the fire and trundle away in it, turning a rotisserie until the meat attached to it was perfectly cooked for the guests over the open fire. Their reward was enough meat to keep them alive, and they returned the next night like true professionals.
Not all dogs could assist in the hunting of game like their forebears had, so - before they became revered as pets - dodges like this were their only way to survive without the kindness of strangers.
Theo - like L.T. - was a true professional. His expertise was sniffing explosives. Some of his mates can pick up on the chemicals released just before their master/mistress has an epileptic fit, but it's the same sort of skill.
Somehow, it is even more sad that L.T. has copped it in Helmand, when his beloved dog seemed to voluntarily follow him.