Hello; I was going to argue that a good wall will stop some and slow down others. An analogy. Say I have a large boat with lots of leaks. I patch the bigger holes first and if a big leak is slowed to a trickle, then I am better off. I move on to the other leaks and if I am good enough can stop some completely.
A crummy wall won't stop much. A mediocre wall will stop more. A good wall will stop more. I am retired and watch too much news and talk programs. The tunnels are known about and can be dealt with to some degree of success. I get the feeling a decent border barrier will include more than just a wall. 100% success may not be possible, but we can sure slow it down. I also like the notion that it can make it harder for the illegals to sneak into the country.
Another effect of enhanced border security and wall talk is reported to already be having an effect. I believe there are reports stating fewer are trying to come in already. Obama put out the message to come on up and illegals surged in for a time. President Trump puts out his message and apparently there are fewer sneaking in already. A decent wall can and likely will help.