Hi, to anchor down a polytunnel, I would use temporary fencing pins, and strong webbing, knock the pins into the soil at an angle pointing away from the sides of the tunnel, as deep as you can, then fasten 1 end of the webbing to 1 side, throw it over to the other side, and fasten it to the other pin, do this as many times as you think necessary.
The webbing is less likely to tear the polythene sheeting than rope would be. Derek.

Thank you Derek. Think I will get a cheap one and try the
fencing pins to see if its effective. Am also planning a 2 ft
wide border along the other fence for some Early Nantes
Carrots, and 'Turbo' Onion sets around the flower beds.
I will never be able to balance without holding on to a support again, have to think my way round problems.
Just want my chemical free vegetables again !

You get what you pay for. I use to have a Guardman polytunnel, 9'x6' cost £90. It was wonderful and did exactly what I wanted - except over a five year period I went through two frames and three covers! The green covers are of very poor material and it is not possible to get them tight enough to the frame. I now have a 10'x6' greenhouse in its place.

Thank you Bulbaholic. Am still looking. Heard there is a
small polytunnel with fleece covered frame.

Where I live, polytunnels seem to come and go quite quickly for this same reason. We are very exposed on a moor above the sea. Nothing to shelter us from the westerlies, and the occasional easterlies. I have a greenhouse. It has stood up to everything the weather has thrown at us...so far!