</font><font color="blue" class="small">( <font color="blue"> How far underground are the survey stakes and how might I find them other than buying a metal detector? </font>
My FIL is a retired Civil Engineer and I worked for him over the summer while attending college. We did a lot of surveys and subdivision plans. As others have mentioned, stakes are placed at all corners and changes of direction. We also placed them every so often on very long straight runs. We used 2" square oak stakes with a small tack in the top or concrete markers with a brass medallion on the top, depending upon how much the customer wanted to pay. I can't recall ever using re-bar (it's not wrong to use re-bar, we just never used it). No matter what the marker material, it was always 'planted' flush with the ground surface (so it could be mowed over) and a guard stake pounded in nearby that had colored ribbon tied to it. In the case of a marker in a roadway, we used large head (size of a nickel) nails with ribbon folded up underneath the head and tied a ribbon to the closest tree/bush. In no case did we bury the marker. However, if it's been a long time since the survey was done, some of your markers may have been covered over.
As others have said, look around the areas that are easy to access and that appear to be a property line between your land and a neighbors. Fence posts, walls, hedge rows, etc. are all good places to start. )</font>
Around here the surveyors all use rebar, with their own custom plastic caps with their registered surveyor number on it. I've seen them in red, yellow, and silver on several diameters of rebar. I've seen them use a nail and ribbon for a temporary marker, as for under their theodolite. They carry special metal detectors to find the steel pins (regular metal detectors don't work nearly as well). Older surveys use creeks, trees, rocks, and fencelines to mark boundaries. Magnetic North has moved a lot over the years and not all bearings were properly corrected for declination.
It's very hilly here, but not all the surveyors seem to understand three-dimensional geometry. I had one use the wrong tree for a corner because he said when he tried to use the "right" one, the boundaries woudn't close (on paper). The lot had a steep hill in the middle of one line, and I watched him measure the distance up the hill and back down the other side. I understood the problem, but, hey, I'm not a registered surveyor!