Underground/buried connection

[jumpjamesjump]

Hello all
I have been called out to quote for a garden job where the builder has run a 6mm armoured cable out to the garden, it's not long enough for it's final destination though and so I want to connect onto it, extend it and bury it. Never having buried an outside joint before what is a good product for the job? I see there are a variety of epoxy resin options but I can't seem to find one that I can easily maintain the armour's continuity.

Any suggestions much appreciated

 

[mattg4321]

I must've fitted hundreds of resin joints with no failures.

It's the only sensible choice here.