I've seen the fenced in "picking grid" idea that Bobby mentions. Actually it was a deer-protected
apple tree that got Himalayan blackberry[Rubus discolor] canes grown up to a height of approx. 10 feet inside of the 5x5
deer cage. It worked pretty well for keeping the blackberry canes erect and pickable from outside the cage. It didn't work so well for making the
apple fruit pickable. ha ha.
One thing you may want to look into, is identifying exactly which blackberry you are dealing with. In our area, the
native blackberry [Rubus ursinus] is entirely less invasive, smaller thorned than the Himalayan. It can be handled without leather gloves, which is a must with the tougher berry. We have to dig Himalayan up from it's
underground trunks sometimes with a digging steel or a pick axe, and watch it all night long with a flashlight so that it doesn't touch down and
root itself from the top of the cane bending over near the ground. It's reported they know when you go out to a friend's house for dinner, and use the opportunity to root then. For anyone considering desperate measures, the selective use of super-concentrated acetic acid to burn the roots can be a tool to use. It's not patented by Mon-Satano.