I'm right there with you as far as the red clay goes. I've had plenty of detectors that struggle with it. The Explorer is pretty well known to do good in highly mineralized soils like the gummy red stuff we have. What kind of problems are you having? Is it just nulling out all the time? You might need to lower the sensitivity or use Auto sensitivity to cope with it.
Also, old home sites are known to be really trashy, and the Explorer is a very SLOW processing machine. Make sure you move the coil really slowly or you'll get alot of masking from the iron trash. You'll go into a threshold null and miss a goody next to iron because the machine can't "reset" fast enough. Do you have a coil that's smaller than the stock 10''? If so, you could try it in the trashy areas.
All in all, it sounds like your problem is more because of the trashy conditions than the detector struggling with the clay.
w
