
The perimeter could be a slab path, discourages digging under the fence, and with concrete gravel boards holding panels above ground level prolong fence life.
A friend of mine put in 12 inch gravel boards as she found that was just the right average pee hitting height to stop the panels rotting for our breed.
Also use slabs for the main routes in and out of the house and with the perimeters this covers the most used areas.
Then you could alternate slabs with the slate chips in between, which gives drainage, but the light coloured slabs will keep things light.
Thsi seems nice and will give good drainage, and is large enough for cats to avoid.
http://www.dandystopsoil.co.uk/Building-Materials-Sand-and-Hardcore/Drainage-Gravel-20mm.html?jos_change_template=GRAVEL&pop=0