See if two jute or coir liners for troughs works.

tj

That would be my suggestion as well. Here, they sell it on rolls by the foot or the yard.

Or landscaping fabrics. I hung flower boxes on my fence and planted lettuce in them. The bottom is chicken wire lined with landscape fabric. Hoping I’m smarter than the slugs.

Or burlap, as long as it’s not synthetic.

Burlap will disintegrate. I reuse the landscaping fabric year to year.