This the heart of the matter...
"The steel bollard design is internally reinforced with materials that require time and multiple industrial tools to breach, thereby providing U.S. Border Patrol agents additional response time
to affect a successful law enforcement resolution. In the event that one of the steel bollards becomes damaged, it is quick and cost-effective to repair.
Nothing full-proof. But if it takes folks a long time to pierce a barrier, the objective is achieved.
Tunnels are more likely to be used by criminals, IMO.