There exists already 650 miles of steel barriers/ razor wire, etc. on the border.  There has been a decline in  illegal Mexicans crossing the border and an influx of Mexicans returning to Mexico.  The "estimated" number of 11 million, who knows how many are Mexicans?  But suffice to say a majority of that number have been living in the US for 10 years plus.  Obama did deport over 2 million people targeting the worst (criminal) offenders and ones caught in an 100 mile radius but with clear cut instructions.  Trump and his team unrolled a very chaotic immigration ban that has left the system in shambles and even with the courts repealing that ban he has empowered Border Guards and ICE to continue profiling and detaining legal US citizens and legal Visa holders so that it becomes a "witch hunt".  That is the crux of the problem.  He hasn't as of yet worked out what will happen with the DREAMERS. (DACA).