GPR or Resistivity to locate hidden caves?

[Reckonings]

So I have found some hidden underground caverns or caves if you will. The old fashioned way. Research, then go out looking for land features that look odd or sunken in, or this time of year when it's raining you can look for ground water disappearing in to the earth, then you just start poking and digging. It is time consuming and sometimes you may be in the right place but you poked around and dug for hours, days, and weeks and you can't find what you are sure is there. I am on a hunt that I must get to the bottom of. I have never used GPR or Resistivity equipment although I have downloaded some software and familiarized my self with it and it's operation the only thing I am lacking is data. Does anyone have any of this equipment? Does anyone know where I could rent or possibly buy this equipment? What has kept me from buying in the past is price. I would really like to rent it for a week with or without an operator. If by chance someone on here owns some of this equipment, I would be willing to pay you to come out and help me, this will come with the added bonus of being privy to what I am hunting for with the understanding that this is hush hush. The property is owned by me and the property next to mine I have permission. I would appreciate any lead you could give me to people with this equipment in my neck of the woods which is southern middle Tennessee.
Thank you and Happy Hunting

 

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[Jim in Idaho]

I've been using resistivity for prospecting this summer. I tried straight resistance testing, which would work pretty good for caves, but suffers for metal prospecting. I built my own sending unit, which was inexpensive and works well. I prefer resistivity to resistance for prospecting. Combine that with the free "res2dinv" software and you can get a good picture of what's under the grass. The only downside is you need to have a good idea of the resistivity of the rocks in the area you're prospecting, so the picture the software provides has real meaning in terms of the type of rock it's showing. I'm still working on a test setup for that. Just bought a small lapidary trim saw so I can cut small test pieces from the rocks I collected and brought home.
Jim