unicycling the Water of Leith

Hi There
I’m a unicyclist in Edinburgh (Scotland) and i’m just starting to organise a charity Unicycle on The Water of Leith through the City of Edinburgh. Very early days yet but i’m aiming for March 2009 . All monies going to Marie Curie.
I’m aiming to do it myself in about 5 hours (13 miles) though have never ridden for this long , imagine will have a sore arse. Any advise or interest out there