When you're looking for the outer grass edge you just need to idle around points and watch your sonar. The visible mat usually disapears at a uniform depth all the way around, basically giving away a depth change at that edge. The same is true of the outer edge, when you idle out from the visible edge you will be seeing stalks of grass on your sonar until you reach the depth where it goes to a clean bottom, this is basically the point that light penetration becomes too weak to grow grass. Whatever depth that is should form the edge of the grass pretty much everywhere else on the lake assuming water clarity is similar so you can start targeting points, humps, structure in that depth. That's what works for me, on the outer edge you can't see the grass so it seems easier to lock onto a depth contour and follow that.