"David W.E. Roberts" wrote in message
...
Thanks for that - some things I didn't make clear:

Given what you've clarified, I think I'd not bother at all. I was thinking
about how the services could be replaced in the event of a fault, but from
what you're saying, it rather seems as though the utilities would need to go
for a different route altogether. It might be prudent if there's enough
space to lay concrete, then just a little soft sand around the services then
concrete up to the top. What you need to try and prevent is a sharp edge
from one of the bits of the ballast coming into permanent contact with
either of the services.

You can get gas and electric warning tape, try the electrical wholesalers or
BM's.