Tim- if you fly off of grass you need a fairly large plane so 2.75in. diameter wheels don't look silly. Of course if the field is like a golf green it's wonderful. But any oversize turf needs big wheels.
the wheels also have to be a bit further forward on grass. Make adjustable gear, or gear that is swept half an inch and can be turned around to put the wheels further back for pavement.
We fly almost every contest off of grass, but I use the same old wheels I use all the time - 2 1/4 Dave Brown Lectra Lite, and without adjusting them from the normal pavement settings. It's not like the 2007 NATs but it's not a golf green, either.
One mistake people make time and again is to try to make the gear higher for grass. All that seems to do it cause it to tip over more easily.
It's really all about technique. Over grass you want to take off quartering into the wind, so you can control the pitch angle right from release, and lift off at as low a speed as possible. I you try the usual dead upwind or dead downwind position used on pavement, the tendency will be to nose over. Also, you need to be able to control the airplane accurately at very low altitudes, meaning it needs to be very stable even at low speeds. You need to pop the airplane off the ground as quickly as possible, but only go to about 3-6 inches (with the wheels either just grazing the grass), then level out to the normal *very slow* climb rate. That means you will be within a foot of the ground for about a full second, and you have to be able to do it without any sort of obvious control corrections.
Same thing with landing, you want to slow more than normal, and start grazing the tips of the grass right at dead downwind, and then float it in very slowly as you come around into the wind, to reduce the groundspeed as much as possible before you get into the grass heavily at about 60 to 90 degrees past dead downwind. Again, at the 2007 NATs, the 600x600 pad was about 6" high coarse grass, and the guys in intermediate kept trying to land 90 degrees before dead downwind as per pavement, in a substantial wind (10-12). They were going fast WRT the ground, but with relatively low airspeed, and they would touch and flip almost immediately, over and over. I gave a little instruction to some of the guys who would listen between rounds and sure enough, they were able to manage it without too many "incidents".
Brett