Raspberries are escaping their raised bed after two years :( I really don’t want them to spread beyond it. what to do? Bury a tarp under the mulch? Dig a trench around the bed? Roundup?

Raspberries are escaping their raised bed after two years :( I really don’t want them to spread beyond it. what to do? Bury a tarp under the mulch? Dig a trench around the bed? Roundup?

We have a raspberry in our bare soil and we only had to pull a few in the spring. Good luck!!!