Here's some philosophy 101 for you. See if you can make the connection between this fallacy and your argument that 'walls work'.

Hasty Generalization

A Hasty Generalization is a Fallacy of Jumping to Conclusions in which the conclusion is a generalization. See also Biased Statistics.

Example:

I've met two people in Nicaragua so far, and they were both nice to me. So, all people I will meet in Nicaragua will be nice to me.

In any Hasty Generalization the key error is to overestimate the strength of an argument that is based on too small a sample for the implied confidence level or error margin. In this argument about Nicaragua, using the word "all" in the conclusion implies zero error margin. With zero error margin you'd need to sample every single person in Nicaragua, not just two people.