The U.S. Border Patrol told its agents Friday that when they confront suspected illegal immigrants crossing the frontier who throw rocks a them, they should try to take cover or move away instead of immediately opening fire, Reuters reports.

According to Michael J. Fischer, head of the Border Patrol, immigrant smugglers were increasingly using rock-throwing as a way to drive away patrols. Since 2010, agency personnel have opened fire 43 times, killing 10 people, in response to 1,713 rock-throwing attacks against them. Three officers had been killed in more than 6,000 assaults on agents since 2007.

In the directive, Fischer told agents not to open fire “unless the agent has a reasonable belief, based on the totality of the circumstances, to include the size and nature of the projectiles, that the subject of such force poses an imminent danger of death or serious injury.”

The directive also said that agents should not fire on “a moving vehicle unless the agent has a reasonable belief, based on the totality of the circumstances, that deadly force is being used against an agent or another person present.” It told supervisors in the Border Patrol to use alternatives to deadly force, including equipment to deflate tires and using “less-than-lethal equipment.”