2000 Explorer rusted freeze plugs

I have replaced one freeze plug at 60,000 miles and now have another one that is leaking at 77,000 miles. Is this common? Vehicle is not driven off road and I don't live within 400 miles of ocean. Is there any harm leaving plug and keeping an eye on coolant level? Leak is minimal - size of quarter every night or every other night. Any info would be helpful.