Zillow is very useful for metal detecting. It is a website used to find homes for sale, but it will also tell you the date of when almost any house was built. To find the date of a park, you have to type in the address of a house near the park you want to hunt. the park's address wont work because the park will never be for sale. on the map, click on houses near the park to find the date of the houses. This will tell you the date of when the park was made, but you have to find multiple dates because some houses might have been built recently.