"Jonathan" wrote in message
...
For the past three years I have been building an Anglo-Saxon castle in the
garden of my house, using only traditional tools and materials.

Having laid the foundations and dug the moat, I would like to fill the
moat so as to test its integrity (both of itself and against invaders)
before progressing to erecting the walls....

I suggest you contact the Ministry of Defence. They have recent experience
of using moats to protect buildings, although these days they are designed
to look like ornamental lakes.

Colin Bignell