you can buy 12 or ten gage house hold wire...2 plus 1 where it has 2 
insulated, and one uninsulated wire in the sheeth.  It's fairly inexpensive, 
and all you need to do is cut a slit down one side of the sheeth to pull out 
the bear ground wire.
This is not a lightening ground, but a shack ground, so you can barry the 
bear copper in the ground without negatively effecting much of anything.
I guess the thing about not having the antenna ground close to the shack 
ground is because if lightening ever hit the antenna, it could jump across 
to the shack ground and kill your equipment or something.
but we have to do what we have to do with the situations we're in, so just 
put the shack ground rod where you can as close to the shack as possible and 
that's all you can do.
I assume the reason it has to be barried is for the convenience of the lawn 
mower?

73
Colin, V A6BKX