Gravel border question
 

Hi,

I just had a quick question - I've got a patio in my back garden with a border around it (about a foot wide) which I'm planning to dig down a bit and cover with gravel. The problem is I'm not sure how deep the gravel should be, which obviously effects how much I need to buy - any ideas on a recommended depth? Also, do I need to put any kind of underlay underneath the gravel or will it be fine just laying it on the soil?

Thanks in advance for any help
Alun