how deep/tall?

The price on landscape timbers has finally dropped, so I'm getting ready to build my new raised hop beds. I'll prep everything this summer, and transplant late winter before they come out of dormancy.

How deep will rhizomes go before tunneling under an obstacle and popping up on the other side?

I know the roots can grow very deep, but the rhizomes typically grow horizontally near the surface. I want to lay enough courses of timber to fully contain each plant, but don't want to waste money, effort and soil installing extra courses that aren't necessary. I'm guessing that when they hit an obstacle, most of the time they'll turn towards the surface. I just don't want to deal with the ones that head down instead, then pop up in the middle of my yard a year later.

I had mine in two temporary locations for a while. One was right where the patio, lawn, and the planter next to the house is. The planter and lawn are separated by concrete curbing and I still haven't seen any hops trying to come up through the lawn.

My other temporary location was over in the corner of our yard where the previous owner had put down some 12x12 concrete pavers. I pulled a couple of pavers up and planted my hops there. When I finally built my trellis I dug them all up and moved them to their permanent home. They had sent out a ton of rhizomes under the pavers, but none of them were more than three or four inches down.

So long story short, based on my experience they don't tend to burrow under obstacles much.