You clearly don't understand the problem.
First off, Border Patrol is apprehending a lot more illegals under Biden than they did under Trump.
Most illegals come in at legal ports of entry, not out in the desert. They either present themselves as asylum seekers, or enter in buses with fake papers, arranged by the large agribusinesses who need them to work in the fields. In the latter case, those who bring in the illegals are big Republican donors, so Republican policy is to make big noise, but not stop the labor supply.