Calm down Greg. I think it was 5+ years ago that we first tried the BBB method. Based on that success, it has been used on all but two projects, both of which were in locales that did not have soil issues where we would see migration of rock coming upwards. My 90% estimate is about right. If you re-read my rationale for using a hard-based liner I think it will answer any questions you still have.
It seems one of the concerns (I think that's the right word) in this thread is whether specifying BBB, or any liner method, is somehow throwing costs to golf construction work unnecessarily.
1. A lot of bunkers need liners because they are built in areas where contamination between sand and what is underneath will rapidly ruin the bunker and this will lead to adding sand, re-building and potentially undermining drainage. So, form this perspective, liners are good in these situations (e.g., certain soils). Not every course is built on pristine sandy soils with no rock, clays, etc.
2. Once a liner is determined to be a good approach, the choices are between soft liners (fabrics), hard liners (such as BBB), sprays that seal native soils, or sod placed below the sand layer. Based on my experience with all (except the sod method) I have concluded that the rock (BBB) method is the most reliable.
3. An important factor is cost. Again, in the west where most of my work takes place, gravel is readily available and we have found that the BBB method is about the same as using any of the other methods.
Rebuilding bunkers is costly. In an average capital budget (per year) it is not uncommon to have $40,000 being set aside to re-work bunkers. This is based on $350,000 worth of bunker work at a 7-8 year lifecycle. Of course not all clubs set aside enough for renovation work. What we are trying to do is look for ways to add life to golf course infrastructure ... hard liners like BBB are just one example. Another example is HDPE pipe, which lasts four times longer than PVC.