Hi Joy, I have been giving this some thought over the last two days. Problem is, I don't often do serious!
It seems to me that the encounter in question was a one to one thing, with no one else about until Robin blew his horn and called up the Merry Men. That being the case, what you need is two songs, one a soliloquy for John about guarding the bridge, and then a bragging song as a duet between John and Robin leading up to the fight on the bridge. This could then be reprised as a Chorus Song by Robin, John and the Merry Men after R has been pulled out of the drink (Real water if you can manage it).
Can't think of anything for the soliloquy at present but will keep trying, The bragging song, I keep finding 'The Sporting Races of Galway' going through my mind:-

Oh my name it is John Little,
Tho' I'm oft called Little John......

There I stick at the moment But as the man said 'I'll be back!'

FC