Restricting roots on a raspberry bush

Hi All I have a neighbour who has planted raspberry bushes around 6 inches from my fence. Whilst I quite like a raspberry I'm not so keen on the runners appearing amongst my hellebores and my herbacious border. They seem to spread at quite a rate they have only been in the ground around 18 months and I'm digging out runners on my sided 3ft away and it is a nuisance.I have been advised to dig a trench 2 spits deep on my side and use a root barrier to prevent the roots spreading. I am on a tight budget and just wanted to make sure whatever I put down will do the trick. Any suggestions would be very much appreciated.

Weed killer works wonders.

HaHa thanks Linda though I would rather avoid weedkiller if possible.

Could you use the geotextile weed matting that some people put on borders before putting bark mulch on to stop weeds coming through.  I guess you could fold it in two to double the thickness? It's permeable so will allow moisture back and forth but should keep out the runners.
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