The wall Trump wants to build is symbolic. It has zero chance of making any difference in regard to illegal immigration.
The solution to our illegal immigration policy is to allow much more immigration legally and to provide the infrastructure to process the people coming in. The biggest benefit to switching to a legal immigration system instead of our current system that makes illegal the workers we need in many industries, is that we can set the criteria and prioritize the types of immigrants that we want, while providing the workers we need via a legitimate path to entry.