Blocking suckers with Comfrey or other edging?

Hello,

I'm currently in the middle of converting our back yard into a densely planted, mostly perennial garden. My neighbor who prefers a 'weed' free green lawn has planted a young cedar hedge along their side of the property, whereas I have planted bushing/clumping perennials like sea berry and black berry. However, I know these plants can/do send off suckers, some of which might make it into my neighbor's property and upset them or risk them using chemical control on the edge of their property. Trying to be a good neighbor about it, does any one have any creative ways to help block/reduce the amount of suckers that might make their way to unwanted areas? Will their cedar hedge be enough? Will densely planting a row of comfrey help block suckers from making it through? Do I need some sort of underground solid barrier, if so, how deep do suckers tend to go?

Thanks!

I have used comfrey to block plants that spread aggressively.  It even blocks quack grass well. I use a double staggered row of comfrey around any area I want to contain,  or that I want to protect from plants that would invade.  I've been very happy with the results.

It depends on the variety of blackberry you have, some that are more close to the original wild stuff are unstoppable, absolutely nothing can stop them from sending offshoots, I have the same problem, and I just get back what have tried to escape in my neighbors which like to spray roundup on the edges, which makes me even more alert on checking about it, blackberries have turned parts of my yard into impenetrable mini jungle, I planted trees near them which will shade them and hopefully I will be able to pass after some years.