Mark BR wrote:

I looked at the non-slip paint, but it is about £28 for enough to cover some
200 sq m. I only want a cover 2' by 1' protected!

Non slip paints are really meant for indoor use, and they aren't very
good when used outdoors, I've found. One option is to use ribbed rubber
flooring material. I have in the past used this outdoors successfully by
first painting the area with thick gloss and liberally spreading sand
on it, to give the underside of the rubber something to grip to. What
you have to do is cover the paint completely with a layer of sand (don't
just sprinkle it) then put a board over it and walk about on the board.
The wait til it's dry, then brush off the excess. Then hose it after a
day or two so there's absolutely no loose grains. The rubber mat can
have ordinary aluminium carpet edging strip around the perimeter. This
will grip the rubber firmly. Fasten the strip down with self tappers.

An alternative to the sandy paint is Evode impact adhesive, but an £8
tin will only barely do 2 sq ft.

Whatever way you fasten the rubber, warm it first because otherwise on a
hot day it will form ridges. It needs to be under v slight tension.

Bill