Stag beetles seem to respond to conservation measures, and this page lists quite a few ideas suitable for open spaces. For gardens in particular I highly recommend that you have a look at the pdf of the PTES Stag Beetle Friendly Gardening brochure.
The creation the piles of logs half buried in the soil has been extremely popular and it has spawned many new names: log pile, loggery, lollipop, pyramid, etc. The latest is logarium, see below for more.
The first link - Stag beetle nests - illustrates how opportunistic this species seems to be. Through my research in an urban environment I've come to the conclusion that stag beetles in favoured areas respond well to a dynamic management, that is, cutting and planting trees suits them.
Well mulched man-made stag beetle habitat. Neuchâtel, Switzerland. Photo by Sylvie Barbalat, May 2007.
Conservation tip! All stumps and log piles benefit from regular lavish mulches of hard wood chips. So if you live in a stag beetle favoured area we highly recommend you to do this. I've done it myself, see Stag beetles in my back garden.