Crossing the River challenge

Here's the original problem (from Sarah):

The five FAMILY family members and their five dogs (each family member owned a dog) were hiking when they encountered a river to cross. They rented a boat which could hold three living things--people or dogs. Unfortunately, the dogs were temperamental: Each was comfortable only with its owner and could not be near another person, not even momentarily, unless its owner was present. Dogs could be with other dogs, however. The crossing would have been impossible except that Lisa's dog had attended a first-rate obedience school and knew how to operate the boat. No other dogs were that well-educated. How was the crossing arranged and how many trips did it take?

And here is a solution:

Let the five people be represented by A, B, C, D, and E. Let the five dogs be represented by a, b, c, d, and e. [Let Lisa and her dog be A and a, respectively.]

a, b, and c cross the river. a comes back alone and takes back d. a goes back and says behind while B, C, and D cross the river. Now A, a, E, and e are on the starting shore, and B, b, C, c, D, and d are on the destination shore. D and d return; A and a cross. C and c go back, and C, D, and E cross. Now dogs c, d, and e are on the starting shore, and everyone else is on the destination shore. a goes back and returns with c and d, then goes back and returns with e

I modified the problem so we had five knights on a quest with their noble chargers. The knights and chargers had colored strings tied on their wrists to identify them: green knight and green charger, red knight and red charger, etc. The black charger was the one specially trained to be able to operate the boat. I had the boys physically act out the problem, no more than three at a time crossing from one side of the river to the other and following all the rules. I did give occasional hints when they were stuck. The first group ended up with the solution outlined above, the second group had a similar solution but with a few extra steps.