I managed to get out to the old zoo this morning after work for a couple hours. I thought to give a particular area a try with the TDI because it was nearly impossible to detect with the CTX due to having so much trash and iron. Turns out it was a good decision! Found lots of clad, but finally got past my 1919 wheatie barrier with my first 1918 wheat.
Working low and slow over a hill I got a pretty deep signal. Had to go down about 10 inches and I saw shiny. Been so long I almost forgot what silver looked like. Break up the dirt ball and see a pretty nice 1939 Washington quarter.
The only other notable find was an old Schrader balloon tire pressure gauge which apparently dates from about 1907 to 1926.
Here's a similar undug example: