Mr. Duncan said that holding the buyer responsible was virtually unenforceable.

It became clear, for example, that a contract signed without the artist having had independent legal advice was virtually unenforceable.

The two groups argued that the rules would be virtually unenforceable and would only discourage people from engaging in either activity.

Once in place, Prohibition proved virtually unenforceable.

Paul Wein, a spokesman for the Department of Buildings, agreed, saying the existing regulations were "virtually unenforceable" against these kinds of billboards.

The bill does not provide an exception for women whose health is at risk, and it would be virtually unenforceable.

The loophole is, in effect, a confession that the rule is virtually unenforceable; it may also be designed to blunt foreign criticism.

It would put teeth back into a statute that has been rendered virtually unenforceable, and 45 state attorneys general support it for that reason.

This legislation, if it includes self-employed, will be virtually unenforceable.

"The law is virtually unenforceable, as it is," said a spokeswoman for the Association of Metropolitan Authorities, an organization that represents municipal governments in Britain.