metal detecting is not illegal. however, when you excavate , that is covered already by the rules on treasure hunting permit as mentioned by the national museum law .
when you treasure hunt, as in other countries, you really need a permit.
the problem is foreigners are not allowed to apply for a treasure hunting permit, as i have heard. i am not sure about this. i have to consult the law (national heritage act of 2009 and its 2011 implementing rules).
but foreigners can partner with filipinos on a 60-40% equity arrangement by making a corporation or a partnership. 60% goes to filipinos, while 40% goes to foreigners. same with mining. there is a filipino equity rule when foreigners are involved.
when these corp or partnerships are formed, you can now apply a treasure hunting permit. the law does not state that when you apply a th permit, there must be 100% filipino equity... a caveat however is that you must also file pertinent documents like audited financial statements, register with appropriate agencies. a certified accountant can do that easily.
when you have already been given a treasure hunting permit, the govt is not there 24/7. that is where it gets more exciting. usually, the n ational museum through its partnership with japanese, the japanese would always declare ... oh there is no treasure on your property. so that's it. you have a permit already, the govt says there is no treasure. with that, you can safely conduct your acdtivity but you must report to the national museum from time to time. you are required to submit periodic reports as the permit expires when it reached a specific period.
there is no need to risk your freedom when you do illegal treasure hunting. just like in the US. when you secure permits in the US, why not secure here in the Ph also. but do it clandestinely and smartly. there are so many ways to solve a problem. just do it smartly and do it safely where your life and limb will never be compromised.