Perhaps you should try some spelling variations:
backward tracking » backward facing, backward masking, backward blocking
backwards tracing » backward facing, backwards looking, backward lasing
backward walking » backward masking, backward willing, backward facing
backward framing » backward facing, backward freezing, backward filling

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: ((backward walking) OR (((backward tracking) OR (((backwards tracing) OR (backward framing)))))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((backward walking) or (((backward tracking) or (((backwards tracing) OR (backward framing))))))".
• Adding a wildcard symbol may retrieve word variants: ((backward walking) or (((backward tracking) or (((backwards tracing) OR (backward framing))))))*.