"..........These bag things are supposed to bio-degrade, so only a solution
for a year or so ............"

They are not Bio degradable, it's the Ultra Violet (UV) light that breaks
down the white plastic they are made of. If the sunlight is kept off them
they will last 5 or 6 years.

For your stakes I would get the heavy grade of Roof batons, they have the
advantage of being tanalised as well and should last 3 or 4 years.

I use these bags for the debris from the shredder and leave it in the bags
for 6 months or so to start breaking down, works well, and you don't need to
make drainage holes as the water gets out of the woven fabric quite easily,
and if you have any doubts, try putting a hose into an empty bag and see if
you can fill it with water.

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk