Design is an important part of creating any garden, more so when trying to create a hardy succulent area. I tend to do lots of drawings of the area, measure it up, work out how much sun it will get and finally plan the planting.
One key part of this is thinking about the planting medium and the physical structure. When it comes to growing succulents in the UK the mantra is "drainage, drainage, drainage". It is not enough to simply add gravel to the soil, or even replace all the soil with gravel. There is a big difference between a gravel garden planted with local plants or alpines, and trying to grow succulents from much warmer areas. If you want a truly versatile dry bed then it has to be raised, either by building a wall around the whole thing or using a rockery. There are two reasons for this, the first being drainage. Raising the bed above ground means that if the planting medium is free draining, any water will run straight through and out of the bottom.
The second advantage is that in raising the bed up you have an opportunity to introduce a heat sink. These are increasingly being used in green house and even house design, but are not widely mentioned when it comes to the rest of the garden. I am sure most people recognise that a large rock on the surface will store heat during the day slowly releasing it over night. Multiply that up with a pile of rocks and you have a heat sink which may be the difference between life and death for some plants. In my current bed, I used all the dug up concrete to raise the levels and filled gaps with gravel This extra mass forms the base of my heat sink and I suspect maybe one reason I can plant some the plants in my dry bed. The height and heat sink were increased further with a more sculptural top layer of large rocks, forming the pockets into which the plants where placed.
I am already considering options for my next garden, do I want brick or stone walls, railway sleepers, or perhaps build only the back wall and then slope the bed down to ground level at the front. Then what stones do I want to use? I like the river boulders I have in my current bed, but I have seen some amazing succulent beds using volcanic rocks and darker stones. Finally do I want to include any soil at all? My current front bed is almost pure gravel, but this slows growth down and having a way I can include soil in some location without it washing away would probably be helpful to some plants.
It's only once I get into the new garden and see the space; what shapes I want, and how the succulent bed will fit in with the rest of the space, that I will be able to finalise exactly which method I use. Whatever I end up doing, all the succulent beds will be raised to some degree and will make the most of heat sinks wherever possible.
I should give one warning though. Should you ever come to move you had better hope that the next person wants a dry bed, other wise they are going to have to move all that material back out again!