Here's the problem with tool breakage as it currently stands....
For some reason (and it's something I will be looking into when time allows) the percentages for breakage are somewhat finicky, and small changes can have much greater effects when actually running in game. At the beginning of the year, we saw what a very modest increase in tool breakage chances did to tool breakage, and such chances have been reverted to their previous levels.
If I remember correctly (and I can't check right now) the percentages for breaking tools is actually quite low, and getting it any lower would be making them nearly unbreakable.
At this time, there are much bigger fish to fry, but eventually I hope to have much finer-grained control over tool and spawn breakage. When I get a chance, I'll post the tool breakage percentages, but I think they're really quite low...like around a 1% chance each time they're used.