Usually dogwood cuttings roof very easily. I never have any problems. However,, I think covering with fleece may be a solution. The cuttings need to be kept moist during the summer though. I agree about layering. I prefer to put cuttings in pots rather than into open ground though. Sometimes, if you look around your established shrub, you will see that it already has layered itself and then you can cut down with a spade and dig it up. I did this only last spring and have a new young dogwood in the garden with stems about 4' high.