The following is an excerpt of the side bar to an article by The Daily Times:
FARMINGTON — Nine counties in three states encompassing Navajo land are considering agreements with the tribe to allow police officers on both sides to enforce laws. The agreements are expected to eliminate sanctuaries from the law and increase arrests and convictions.
San Juan County, N.M., is the only county that will not cross-commission deputies with the tribe, though Sheriff Ken Christesen has signaled a willingness to certify his deputies with the Bureau of Indian Affairs to enforce federal laws.
One county already has a cross-commissioning agreement in place, two have signed mutual aid agreements and the five remaining counties are considering their options.
Turtle Talk 
Dangerous or good thing…. has led to abuse…Tribal police have been known to go onto fee land occupied by Indian people and vice versa with questionable agreements…
Regardless, it is the future. Surely the federal government can’t solve the problem.
Slight clarification to the statements made in the article. There are two county cross-commission agreements, with McKinley and Socorro Counties in New Mexico, and one mutual aid agreement, with Apache County in Arizona. Though called “mutual aid” the agreement with Apache is essentially a cross-commission agreement.