When building a patio, you and your landscaper have the option between wet laid and dry laid hardscapes. Dry laid refers to a process that tends to use a sand base (or other dry base) on top of gravel, with the stones laid out on top. Wet laid is when the hardscape is laid on top of concrete slabs that are placed on top of the gravel.
Wet laid tends to be more expensive, and it can be costly to repair should they get damaged, but it does tend to last longer against the elements. Dry laid is much more affordable – including repairs – but breaks down slightly more often in bad weather.