Thanks John, I'm thinking along the right lines. I have one of those relatively powerful pocket lasers that shoots like a mile that I expect to rig and I imagine it'll work well enough.
A good laser level with good level rod is a precision instrument accurate to small fractions of an inch at a couple of hundred feet. A decent manual telescopic type level, tripod and rod can be had for about $230, and will be good to about 1/4 inch in a hundred feet, plenty good for a pond.
A pocket laser rigged to a carpenter level would probably be off by at least a few inches in a hundred feet. I wouldn't trust it much as an accurate building level.
