Q: In the state of Missouri is it legal for a city worker to come into a privacy fenced backyard, when there are no meters

A: Generally, it would not be lawful for a city worker to enter your property without your permission, or to damage your fence. However, there are many circumstances where it is legal for them to enter your property - even against your direction. Having a meter is just one example where a city or utility worker may lawfully enter your property, but there are others such as city code or ordinance enforcement.

A city worker, such as a code enforcement officer, is a government agent subject to certain limitations. Any government agent discovering a code violation, conducting an investigation, or gathering evidence must operate within the limits of the 4th Amendment - namely the prohibitions against unreasonable searches & seizures. An agent entering your or neighboring properties, or observing your backyard is a search.

The legality of the search depends on whether it was reasonable. A search is reasonable if there is an administrative search warrant, or probable cause of an ongoing violation of law. An exception to the warrant requirement is the Plain View Doctrine, which means if there is evidence of a violation observable in plain view then there is probable cause enough to conduct a search without a warrant. What is observable in plain view is pretty broad, and is also determined by whether there was a reasonable expectation of privacy. Having a fence is recognized as establishing a reasonable expectation of privacy, but not a strong one. The US Supreme Court has held that looking through or over a fence, whether chain link or a 10-ft high wood privacy fence, is lawful and anything observed counts towards that plain view doctrine.

So, if a city worker had an administrative search warrant or observed anything indicating the possibility of any violation in plain view, they may have had the lawful ability to enter onto your property directly.