My dogs red rocket looks like two little round balls and it looks like its going to explode

Do you mean his penis? Has he been neutered? Sounds like it could be the bulbus glandis or the knot, happens usually only after they have mated. During mating the tissues swell up and lock (tie) the male's penis inside the female.

That happens when they get (how to put this delicately) excited.

As Bella said, the glands at the base of the penis swell up. It is normal.
What is not normal is if his actual penis is unsheathing itself all the time, or stays out for long periods.

I have noticed one of my males swells after we have been play fighting... I think I was was the only one 'fighting'.

Might I suggest having him altered. This will not only get him into a vet to be certain does not currently have any infections but will eliminate many many infections of his genitals down the road not to mention help him keep his "rocket" in his pocket. :)