It won't go down. If you try to do that, it will eventually die back to the highest point on each cane. I just let them keep on going on their own and wave around loose up there. Often they will arch over some. Jeri

Fourth of July -- Tom Carruth's red and white striper -- is said to be hardy over a wide range of climates. Might think about that. Jeri

Don Juan is a climbing rose that grows typically at least 10-12' tall & 8' wide. You're concerned that the Knockouts will eventually grow too big for the space, so just checking in with Don Juan's eventual size. Since you plan to train the long canes horizontally, the height will be reduced by adding to the width. Jackson & Perkins recommends planting 8' apart for solid coverage. ( http://tinyurl.com/mr5r7a8 ) Click on "plant description" at that link for further details. So I'm with kippy & brittie here that you wouldn't need more than 2 for your 15' fence. Though you're thinking of trellis to space the roses away from the fence, consider the suggestions of boncrow & kippy for espaliering using the fence. Eyebolts of appropriate length can be screwed to the fence to hold horizontal runs of wire, or blocks of wood or whatever can be attached to the fence at right angles to project from it to hold shorter eyebolts for the same purpose. (And light to medium weight trellis can be attached in the same manner from the fence.) This is the simplest, least expensive & most unobtrusive method. Canes are lightly tied to the wires with soft material, as you probably saw in the videos, in a figure 8. Check out kona's photos - 3rd & 4th down on the left in the link below - to see how this has been done. There are only two runs of wire. While you're there, check out all the photos of this lovely rose & the ways it's been grown. Here is a link that might be useful: Don Juan photos This post was edited by vasue on Sun, Aug 31, 14 at 19:38

Choose your favorite support for espalier, fan it out on that and tie it in. Of course, getting started would be a lot easier with a young small plant that didn't have a comparatively big bushy top.