If you are wanting a temporary solution it will depend on the firmness of the ground what preparation you may need. If the ground is level enough and firm then the slabs can be placed on the surface of the ground. If the ground is boggy or uneven some digging out and compaction may be necessary. Obviously their tunnels will need to be filled in and compacted down before the slabs are laid.
You could put a geotextile membrane down but this is only essential if you are bothered about weed growth through the slabs. If you are not mortaring the slabs I assume you will butt them up to each other anyway.
Feel free to post a photo and we should be able to offer more specific advice. For the best solution mark out the area to be slabbed and then dig down about 5cm and compact some sharp sand to form a "bed" for the slabs, and then butt the slabs up to each other. A membrane under the sand will stop anything coming through, but make sure you double over the edges by at least 10cm to avoid anything coming through any gaps.
Let us know how you get on