Be sure and read through the entire page at this link. ARPA and You
Even though ARPA does not specifically mention "metal detecting", you need to understand what ARPA says about digging artifacts.
The laws were written to protect relics on Indian lands. But unfortunately they broadened their scope to include any artifact more than 100 years old.
In addition to the above mentioned ARPA law, if you are detecting in New Hampshire, you must be aware of another law,the National Historic Preservation Act. (NHPA)
As confusing as the above laws may seem, if you are detecting in New Hampshire,
Do not dig anything that you believe is an artifact, or anything that is older than 100 years.
Especially if you are on any State Lands.
Do Not Give Up The Hobby
Many have said to me that they are tired of the laws that restrict us from metal detecting, and they are ready to quit the hobby. I tell them if they do, then the beauracrats who make these laws, and the Archaeologists who defend them, will win. If you happen to be thinking this way understand that for many years we have had these laws, and the hobby is still going strong.
Metal detecting on private property does not come under the above laws.
If you want to detect on private property, then be sure you get written permission from the landowner.
For detecting in New Hampshire, town, village and city parks, you'll need to check with those local officials.
I cannot be responsible for any outdated laws from the time of this posting.
My home page is all about metal detecting in eastern ghost towns.
Have you tried metal detecting in New Hampshire ghost towns?
Remember, don't give up the hobby because of a few laws. There are still many places to detect.