What is your opinion apout this topic ? http://mashable.com/2013/03/23/bill-gates-condom/ I laughed about 2 minutes but then I realize I could get a big prize for a simple idea. )
The problem with a condom is that it covers the whole shaft, when it only needs to cover the hole. If you could have something catch the sperm from the hole without covering the whole shaft, then this would be best.