Newspaper works well. Use about 4 sheets of it and make sure the edges overlap. Wet it down, and put mulch on top of it. It will last for about a year and eventually degrade. If you need to plant anything else in the bed just dig a hole through the newspaper and redo the newspaper around it when you're done. I do this for my rose beds because I'm a horribly lazy gardener. In fact, I usually dig a hole in the grass, plant my rose, and newspaper around it. I still get some grass coming up but it's not that bad and I can just pull it. There's a spray called Grass be Gone by Ortho that is safe to use around roses, but it didn't work too well for me when I tried it last year. I'm trying it again this year but I haven't had a chance to use it yet.

The part I would worry the most is where it stops at the sidewalk. If there was some way of putting another course of the stonework across there to stop dirt/debris moving out of the garden onto public space I'd feel happier (if it were mine.) I don't know if you get snow in winter, or interesting frosts that affect your steps. What impact would having a raised bed there have on your ability to clear snow? If the mulch stays in one place (apart from the birds helping it to move) then you shouldn't have a lot of runoff or downhilll movement of soil. You don't say what you plan to plant there. In my own zone I could think of natives that would tolerate that depth of soil, despite the rubble below. And heaps of weeds, too. Not to mention shrubs and herbs. I'm just thinking that stooping over from the steps to garden could be quite demanding. I like your wood constructions. And I like that blockwork you have out front even better as a match for your house. As well as this forum - you could offer the idea on some of the other forums that get more traffic than this one. PS Love your boulders! They look sort of glacial. Very pretty!

Contrary to common wisdom, putting gravel under the soil will make drainage worse. So save all that labor for a different project. Why do you think it stays so wet? What kind of soil or soil mix is in the planter? How deep is it?

I've read that is works.