Regardless of my personal opinions about issues like gun control, legalization of drugs, and guarding our borders against illegal immigrants, many news sources claim it is either too expensive, grossly inefficient, or impossible for the government to perform these functions successfully.
My suggestion is to stop performing these generic activities, and to simply require citizens get licenses for activities like we do today for driving a car. It is illegal to drive without a license or under the influence of drugs.
Violation of licensing requirements seems much easier to enforce.