What happens when there are too many cows and not enough fences?

People deal with it themselves.

Ellickson challenges the traditional idea that law is the loudest and most final voice when it comes to conflict resolution.  He charges that the residents of Shasta county manage their own issues without the assistance of legal intervention.  When someone's cows trespass onto their property they deal with it themselves instead of calling the police or their attorney.  

In other words, people often resort to the use of self-help methods first in an effort to resolve disputes. People exercise "... options of 'exit' 'voice' and 'loyalty' to influence others around them. ... The legal-centralist assertion that the state monopolizes, or even aspires to monopolize, the use of force is patently false"(p.143).

Ellickson, Robert C. (1991).  Order without Law:  How Neighbors Settle Disputes.  Cambridge, Massachusetts: Harvard University Press.