We do not try to "silence the thoughts before they arise" in Skikantaza. It is more that we allow the thoughts that naturally drift into mind to to naturally drift out of mind, much as clouds (of thought) naturally drift in and out of a clear blue sky. In this way, return again and again to the open, clear blue sky.
One of the key points about Master Dogen's approach to Zazen is to allow the clouds (of thought) to drift naturally out of mind (our thoughts of this and that, likes and dislikes, judgments, events, etc) and we come back again and again to the clear blue sky. Do that again and again, 100 billion times and 100 billion times again.
HOWEVER, Dogen taught "non-thinking" (also called "thinking not thinking"). That means that there is nothing "wrong" with the clouds. It is not that blue sky is "good" while clouds are "bad" (some Buddhism and other Eastern philosophies imply that). We allow the clouds to drift out of mind, but neither do we resent the clouds when present or on very cloudy days. Even on those days when the sky is all cloudy, and not an inch of blue is present, the blue sky is still there behind the clouds. WE DO NOT SEEK TO BREAK UP OR RESIST ANY PART OF THE SKY, CLOUDS OR BLUE ... It is all the unbroken sky. Understand?
So, no need to "catch" the thoughts and chase them away, even as we seek during Zazen to find the open, blue sky.