National defense is considered a public good because there appears to be no limits to the nonrivalry-in-consumption characteristic, and exclusion of nonpayers is impossible. Are there any other goods that so perfectly meet both public goods criteria?

Perhaps. Beaches, parks, and public swimming pools all can become overcrowded. It is also possible to exclude (though it may be costly) nonpayers from most public goods, for example, highways. One example that comes close to national defense, however, is produced in the private sector. A radio broadcast never becomes congested, and once it is produced, it is virtually impossible to prevent anyone from consuming it.