You have options of limiting selected sites. One option is to create a calculated field based on the existence of one of the 10 you are looking at being eligible:
CalcField "GoodSite":
CASE [Site]
WHEN 'Site1' THEN 'Good'
WHEN 'Site2' THEN 'Good'
WHEN 'Site3' THEN 'Good'
WHEN 'Site4' THEN 'Good'
WHEN 'Site5' THEN 'Good'
WHEN 'Site6' THEN 'Good'
WHEN 'Site7' THEN 'Good'
WHEN 'Site8' THEN 'Good'
WHEN 'Site9' THEN 'Good'
WHEN 'Site10' THEN 'Good'
ELSE 'Bad'
END
Then you put GoodSite on the filter shelf and select only 'Good'.
Another option is to create a set and use that as a filter using the method discussed at Creating a Filter Using Sets