Thanks for all the tips and advice guys. I thought I'd give you an update on where we're at with this issue...
We decided to go for the method of continuously reinforcing the message of "no/non" and "mange pas" when she started reaching for any stones/weeds/rubbish when out on her walks. It has been a couple of intensive weeks and means having to watch her like a hawk when she's out in the yard, but if she starts to take an interest in the gravel we distract her with a chew bone (which she loves). She is definitely starting to get the message now.
She does occasionally try to sneak one now and again when she thinks we're not looking (at least she now knows it's wrong!), but I'll chalk that one up to the intelligence of the breed!
