Thanks for the reply UB,

I'm more thinking of backing and laying horses in the same race with something like the following scenario.

12 horse race, out of my 4 lay systems it has 3 horses that I should lay and I have 2 backing systems that select 1 horse to back. This is with the backing systems being built on the basis that you don't back any lay selections - essentially its the first rule.

Probably sounds like a silly question if its fine to take that approach but its just something i'm pondering at the moment. Or would your suggestion simply be rather than backing the horse just stake more on the lays?