With thanks to all who responded, I am pasting below the messages I received in response to a request for recommendations regarding metal detectors for relocating permanent plot markers.
- Sara Cairns ************* We have been very happy with the Schonstedt magnetic locator. It can find old buried rebar under several feet of sediment, whereas the standard metal detector you see people using on the beach is virtually useless in that situation. They are, however, expensive - about $700, I believe, although we bought ours several years ago. ************* Most metal detectors works on moving what we called the "head" (sensor) over the ground in a back and forth motion, and you will hear a sound when you come across most metallic object. You mentioned that the area has thick herbaceous vegetation. Would you be able to move the head back and forth near the ground? I think even the cheapest detectors are sensitive up to about a foot so you have some room where you can raise the head off the ground depending on how deep the markers are buried. The price of metal detectors can go above 1K dollars, mostly the difference between the low and high end detectors are the processor that's attached to the unit which gives you more control over when and how the detector should alert you to the types of metal found in the ground. Is the ground in the area you want to work in have high mineralization materials which might give off background noise? The higher costing units have auto neutralization to background noise where as the lower costing unit have a single knob to adjust the sensitivity. All detectors runs off of batteries so keep in mind the run time when comparing different units. In your case, unless there are lot of background noises from mineralization or garbage in the area, I would go for the cheapest metal detector that you swing back and forth as you walk and then use the Bullseye II Pinpointer (see link below) to get the exact location. http://whites.kellycodetectors.com/bullseye.htm <--- Bullseye II Pinpointer http://www.kellycodetectors.com/allbyprice/29-299-allpurpose.htm <--- general cheaper detectors *************** Hello, i used a basic metal detector from National Geographic; its designed for kids but worked upto 3 inches depth in sand. costs like 15-20 dollars and available from amazon.com ***************** I use a metal detector in prairies to find lost wire flags, lost metal poles, and also those magnetized nails that I too pushed into the soil as markers. I had access to this really nice metal detector that was sort of just a big stick, i.e. it didn't have a flat disk at the bottom as the sensor. It didn't work well for me because it was too sensative so it gave many false positives. Maybe it was reacting to metal farther below the surface or something -- I don't know but it was super frustrating. We finally bought one that is marketed to people searching for treasure like jewelry or coins. This works much better because it only beeps at things near the surface rather than sewer lines buried 10 feet deep. On the downside, it has a round, flat detector that you hold parallel to the ground which could get hung up in dense vegetation. It has worked for me in dense prairie grasses and has gotten dewey wet without trouble. The model we have is Fisher M-scope 1225-X that I think we got from a company called KellyCo. I recall that we couldn't find what we wanted in the regular catalogs (e.g. Forestry Suppliers) so we just searched the Internet. I think it cost around $200-300, but they can get really expensive. One of our crew members lost his wedding ring while doing field work (losing something in tallgrass prairie is like losing it in the ocean) and we were able to find it with the metal detector, so it paid for itself rather quickly. *************** I used a Garrett ACE 250 extensively for over a year to recover marked freshwater mussels in a Kansas stream. I attached Nickels to the mussels so I could recover them monthly and record microhabitat data and assess movement of individuals. I was able to get within several meters of the individuals last known location and then search with the detector. On many occasions I found individuals buried an inch or more in gravel substrate. This detector has a pinpoint feature that allows you to detect how close you are to the metal object, which worked great for finding mussels so it might work well for your study as well. As far as durability it seemed to do very well in air temperatures ranging from 19 to over 100 F. It was a little sluggish in the cold but better than expected. Battery life seems to be very good as well (4 AA). This model was light and comfortable, after an entire day of use my arms where not fatigued. One bonus for aquatic work was that I could submerge the coil and stem clear up to the main housing. One drawback is that the main housing is not very well sealed so it may not perform well in the rain. This company does make entirely waterproof versions but for a substantial increase in price. After months of use it still performed well. From my experience I think this is a good value in metal detectors. The companies web site is: http://www.garrett.com/hobby/products/ace250.htm ************
