I seen Tim Horton on a show 1 time talking about this an he showed how he set the electronics an what to look for . Best I can remember is he said they give a rust color on sonar screen when inside sonar cone .I have seen this on Guntersville before an did'nt know what it was then , an it may have even been something else ,could have been shell bed . I have brought them in on lures before several times .