B.D.
I had the same problem with my girls. I'm not familiar with the Gummi Rail, but all of the other ones I tried did not work, because it went over the top, but my daughter would use her bottom teeth to knaw into the wood, too. So I happened to have an extra strip of some fleece fabric from a blanket someone made me, and I cut little strips along each side, laid it over the railing, and tied the strips in between the slats. It worked great, and she just had no interest in chewing anymore...I know with my daughter, even if you put something else that she could chew on, she would just stand there and chew forever if it was something worth chewing on, like plastic. So the fabric worked well, because she didn't want to chew on that.