Rabbits can devastate an area VERY quickly. To keep them out is fairly straightforward and can be done in one of two ways.

Rabbit Netting
Electric rabbit netting is great for flat areas or areas with closely cropped grass. The netting starts off with 5cm horizontal spacings and these only increase to 10cm high after the 30cm mark. This provides pretty much blanket coverage of an area that a rabbit cannot penetrate. The close proximity of the bottom strand to the ground means that the net could be prone to a slight earth leakage if the vegetation grew up and into it. This isn't a problem if using a larger energiser but may affect the smaller models.

Post & Twine / Wire Electric Fence
We've used this type of system as a permanent fence before for football training pitches that were inundated with rabbits. If worked very well but it did need tensioned every now and again. Wooden stakes hammered into the ground at 5m intervals with wire or polytwine at 10cm intervals should be enough to deter them. Using this method, you can hug the ground contours as closely as necessary.

Occassionally the rabbits learn to jump through the wires. As they are going between two live electric fence wires mid-flight they rabit does not receive the shock. The way to resolve this is by adding another line of twine and rather than connecting this to the other wires, connect it to the earth stake. This will cause the rabbit to touch both a live and an earth wire and so receive the shock. If posts are fairly thin garden posts around 2" wide then you'll be okay to run the earth lines on the other side to the powered lines.