It would look most unnatural and weird. The usual top dressing for heathers would be bark chips. These would help keep the weeds down but probably not deter cats. However, in just a few years time the heathers will have spread and there won't be any visible soil to excite the cats.

I would simply hoe the bare soil until the heathers spread.If they are to be summer flowering heathers make sure you check the acidity (pH) of the soil before buying any as they need acid soil. Winter flowering ones are not fussy.

Thanks Bulba and Stera. I had told him he would need to buy compost suitable for heathers as they don't like our heavy clay. I'm interested to hear that winter flowering heathers are perhaps easier to grow and will tell him.
Ok Bulba, I thought it was not quite right to use slate because all the heather I see in our locality is on the greensand ridge that runs through the Weald but I didn't know whether it grew in slaty areas as well.

I should have said not so fussy, rather than just not fussy. Why not play safe, put off planting the bed for a year and just try a couple to see how they like it? Could save him a lot of money. If the soil really isn't suitable he'll need a lot of ericaceous compost to improve it, not just a sprinkle.

ok, thanks Stera. I'll tell him!