Sure preventing logical errors is hard, but it is already an improvement that typical C errors aren't possible.
Limbo does not support this, but both Java and .NET allow for security control at class and method level, however they tend to be misunderstood by most developers, which don't regularly use such features.
There are facilities and standards in most languages to help prevent this, but can you point out why this is not possible in Limbo? I'm not personally familiar with it.