The double fencing built here in the San Diego County has been very effective. The problem now is it has not been completed and the ILLEGAL hordes are crossing beyond where it ends.
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And they use those tunnels. Don’t forget the tunnels. Plus the areas away from population where they use ladders. Fences are only as good as they are supported by people, if not supported they’re just a nuisance that will be gotten around or broken through. Which isn’t saying we shouldn’t have it, simply pointing out that a fence is the BEGINNING not the fix.