Holly hedge advice needed.

I'm planning on planting a holly hedge against a stone wall as a backdrop to a few acers and other perennials. I want the Ilex aquifolium but how do I ensure I get berries? I know you need male and female ones but how can you tell if you have a mixture?

Hello the variegated are easy to identify silver king is the female berrying plant gold queen is the Male  dont ask why the mix up was done years ago   jezza