Gravel is the first thing that comes to mind, using the same kind of gravel throughout to link the rocky areas. Other medium could be grass, bark or flower beds. However, it the rock areas are to be main features I would suggest just one medium to link them all.

Do you mean your garden will be mostly little stones?

Clarification seems to be needed! You've said the garden's an oblong, and you want 3 different kinds of stones in it, and you want to separate them in some way. That rather implies you've got nothing else in the garden, and aren't intending to put anything else - no plants, no trees, no patio, no grass, is that correct?

A good divison is important to contain them and stop them mixing. I contained my side garden stones with Sleepers, looks good and does not move or rot. I also used large rocks/boulders to separate/contain stones and they look good. I recommend a weed suppressant membrane under the stones after you have cleared the area of weeds etc.
A line of pots filled with stones or plants can also make a barrier as can a raised bed or even a shallow dyke of water.
Try looking at Goypeadia photos in 'Sidegarden ideas' there are some ideas you might like as there are on other pages. The Japanese use a lot of stones you might get some ideas from them on line? Good luck with this division as there are some interesting things you can do.

hi, thanks for you suggestions. yes i think some clarifiaction is needed. The garden is large and ablong shape, it has a large old seed spreader in it as a feature along with a few grasses. i thought that adding 3 different kinds of stones somehow contained would give it a totally different look and easy care as well. The shape of the garden is made from small rocks so the stone theme should fit in. I live at the bottom of a hill so i wanted something quite natural to blend in with the background. Drc726 thanks for the websites i will go and have a look. :)

I'm still having difficulty imagining what your garden looks like.

Is it basically going to be 3 large areas of covered stones?

a photo of your plot plus a photo of a simple design you have in mind on paper would help. Also the size of stones/cobbles/pebbles/boulders you might be thinking of would be useful.
Straight away I can imagine tree ferns & cobbles looking superb. If your part of New Zealand would support such plants of course?

I guess a bit more information would be usefull. I was imagining three architectural rocky outcrops of different local stones.