I have tried all sorts of rewrite rules in htaccess but nothing I use works
There's multiple old thread on this topic in both this forum and Search Engine Spider Forum.
Generally speaking though, I found these double slashes were almost always caused by active links in my own pages that I'd missed correcting. The numbers will continue to propagate until your repair your syntax errors on your own pages. There are many html tools that will do these kinds of editing in seconds as opposed to making the corrections manually.