How 'bout putting a layer of fine sand over the peat, this should
also keep it down and still let the U. gibba attach to the
substrate. I have U. gibba flowering profusely at the moment and
mine persist in just shallow water (5cm). While I have not put
any peat on the bottom as such, there is some sludgy peat that it
is attached to.
Just had a thought, some of those compressed peat pellets may be
the way to go.
Cheers
Terry