Several things to remember.
1. If your pulling coins, that park is not hunted out. I hit a tiny park that everyone said was hunted out last weekend, got nothing but modern coins. Then 15ft from the curb near a older tree I got a Canadian 1910 Edward VII "fishscale" nickel.
2. Your have the advantage with the CTX, it can find coins the other detectors null out on or just cannot see if your running in combine mode. Back in February, I was hunting a very old, large park with friends. Started griding a grass area that some of the older guys with me have hunted with everything from E-tracs back to the first detectors close to 40 years ago. I pulled a 1909 Canadian 50 cent piece and 1931 Canadian silver dime in the same hole in the middle of that green space, with a huge piece of rusty wire about 4" near it.
3. Do NOT use ANY discrimination on the screen. Run wide open to hear everything.
4. Dig anything on the 11, 12, 13, 14 lines. No matter the numbers, or scratchy tones; you will find surprises, and at the same time clean out trash that can hide the coins you want to find.
5. Perseverance is the key word. Keep hitting the park areas in small grid patterns like 50ftx50ft. In different directions each time. I do this in ferrous-coin, combine, then switch to ground coin, combine and recently I've added a pass in 2 tone ferrous, low trash for the most depth power. Only then when I get no signals but DEEP iron(sometimes I dig that out too just in case) do I say I've "maybe" "cleaned" that area, at least until Minelab comes out with the next generation of detector to blow our minds and open up the targets again.
Don't give up, listen to the signals, learn the detector. It will win you over totally when you pull something awesome from a so called hunted out park.