The problem is that Spain has already done that, and the “migrants” rush the wall and overwhelm the Guardia Civil and any other forces there. The new government - which is not just old style Socialist, but radical leftist - has invited more ¨migrants,¨ almost all of them Muslims, and Spaniards are very upset. But the left and the leftist press rule in Spain, so lots of luck if you’re just an ordinary little Spaniard.
That’s in Morocco IINM. The border fence at Ceuta is a little over five miles in length and the Melilla one is over 6½ miles long. The fences have been reinforced and the height raised, but Morocco not recognizing Spanish sovereignty in Ceuta and Melilla is no help.