The Development of Currency

At the very moment that I spotted the word money in Chapter 3 of "Who Own's the Future", I instantly thought back to how currency is developing. For example, last week an customer paid for their items with the new one hundred dollar bill and at first sight it appeared to look like something someone printed in their basement. The customer instantly recognized the suspension on my face and explained to me it was the new hundred. Not really taking his word for it, I wrote a few lines on it with the counterfeit marker and indeed it was real. So I gave him his change, receipt, and allowed him to proceed. I don't understand why the bill needs a reflector strip on it with a repetition of small 100 stamped on it, or even an even bigger 100 printed on back than in front. Eventually monopoly money will look realer than the real money. I know this might be a drastic conclusion, but in all honesty how can we expect to stop people from printing fake currency when the real currency has an synthetic concept?