re: How hard is it to actually secure the border?

Difficult, but with even an ounce of effort it could be done much more effectively than it is now. There are several aspects to the border that need to be addressed:

1. What draws these immigrants here?
2. Why do they not use the legal option?
3. How can we physically keep them out?
4. How can such a physically barrier be monitored and enforced?
5. How do we pay for it?

Remember, an ounce of prevention is worth a pound of cure. If you eliminate the free government benefits, eliminate their ability to undercut the minimum wage, and make it easier for them to come legally, you can quickly stem the vast majority of the tide of illegal immigrants. However, it is infinitely more difficult to enforce those things if the physical barriers are not enforced or put in place.