Once again somewhat mystified with exclude rules

[Harry Putnam]

I go thru this every few mnths it seems.  Rsyncs exclude rules are
very sophisticated but because of that somewhat unfathomable at times.

Simplified:
I want to exclude directories named no_bak anywhere in the tree
but only the files under them, not the direcrories themselves.

My exclude rules look like:
no_bak/*
/no_bak/*

The first one does catch directories by that name on the first level
but this one flies right thru:
projects/no_bak/cdbk/
Along with all contents under it.

If I just use:
no_bak

Then nothing (no_bak or anything under) is copied.  Not a real tragedy
but I would like to keep track of where the no_bak directories are in
the mirror too.

*/no_bak/* doesn't do the job either