This is a common rumor or misunderstanding that has become somewhat of an ongoing joke. It was used with President Clinton as well. The joke refers to "cattle guards" as though they are people and suggest that they should be fired or canceled. It is a way to show the disconnect between urban and rural areas. Most citizens in rural areas know that cattle guards are metal barriers which prevent cattle from moving into and out of particular areas. They are often used on highways for example to prevent cattle from crossing. The joke has been used for quite some time through several presidencies.