In my experience, the harder and heavier the wood, the more sinew is needed to keep splinters from raising on the back. One course is sufficient for juniper, for example, but my sinew backed ipe bows needed 3 courses.
If your bows are breaking suddenly, i.e. "exploding", then all the sinew will do is keep the pieces from flying.....unless you use LOTS of sinew (think horn bow). If you're depending on the backing to keep back of the bow from failing before the belly does, there are better materials than sinew......like hickory or bamboo.