Hi there

Am new to all this so please bear with me!!

I'm looking for a hedge that will grow quickly and will be
bushy and dense from ground level up to keep people out.
I've heard about Leylandi but have seen some (I think) that
seem to get bushy only at head height and therefore can let
people walk between the trunks.

I have a stodgy dense wet clay soil like fudge.

Any reccommendations please re. type of plant, spacing, when
to plant and feed, how to prepare the soil and where to
buy in bulk at a good price.

Cheers
Nick