Get a water tank like this one https://growingfruit.org/t/water-tank-repairs/46993 and partially bury it. Be prepared to mow around it. I have never had trouble containing anything in metal for 20+ years. The metal will someday rust out. When you drill a few holes in the bottom for drainage it is possible a root could get out. Keep in mind if a plant pops up by seed or runner it can always be sprayed. You can buy a tank like that at any farm store since it is used to water livestock.
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I worked with a nurserymen for about fifteen years, starting at age eight. He gave me a thornless blackberry with no name, a raspberry with no name. The raspberry is red & prostrate, it runs across the ground fifteen feet then tip roots. I went from rows to a giant patch.
In stead of digging all the new crowns like a normal fruit lover, I mowed between the row every spring. I must have 200 plants by now, in two different patches.
Yes I should have tied them up, but I was busy with another project at the time.
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