For schutzhund, it's best to keep them intact at least through mental maturity (18-24 months of age or older) because that does allow for full drives to develop including aggression (yes there is such a thing as GOOD aggression). Of course, having an intact animal is a HUGE responsibility so make sure you can properly contain him and control him. Find ways to train around bitches in heat (that are also safely contained) or at least around their scent so he learns to mind at the highest level of distraction possible. Don't be tempted to breed him no matter how many of your neighbors ask for puppies! This is a big temptation to resist. Rather, keep attending your club, get titled, get hip/elbow certifications, know your puppy's ancestry, and if your club and your breeder and other people very knowledgeable in GSDs and schutzhund believe your dog is breedworthy, only then should you consider it but there are a ton more factors to consider as well.
Again, seeing how you already fear about your fence, think long and hard about what your responsibilities will be with owning an intact animal and ensuring he cannot get loose. It is not something to be taken lightly!