Military special forces and U.S. Customs and Border Protection special units spent three weeks trying to scale the eight prototypes of President Trump’s proposed border wall, but found the barriers extremely difficult to overcome, according to an Associated Press report.

The testers employed a variety of tools in their endeavor, such as “jackhammers, saws, torches and other tools and climbing devices.”

The testers were unable to overcome the assortment of barriers due to their tall heights, according to the report. They were able to reach up to 20 feet, but required “help” after that. The border wall prototypes are around 30 feet tall.

Only one tester managed to “land a hook on top of the wall without help,” according to the report.

The AP report also details some of the features of the prototype walls that Customs and Border Protection agents favor, including “steel at ground level,” which allows agents to see what is happening on the opposite side of the wall, as well as topping the barrier with “smooth concrete surfaces” to prevent climbing.

Testing on the prototypes could last up to two months, and may result in a wall that combines elements of several different designs, the report concludes.