When you do
@my_page = ::Refinery::Page.find('foo')
it tries to find page by slug first and if it doesn't find it then it tries to find it by id. If you don't deal with localization you can do
@my_page = ::Refinery::Page.find_by_slug('foo')
which will return page if it finds it or nil if it doesn't.
With localization it get's complicated but this should do the trick
if ::Refinery::Page::Translation.find_by_slug('foo').present?
@my_page = ::Refinery::Page::Translation.find_by_slug('foo').refinery_page
end