For a more recent discussion about a similar topic check this question out.
What\'s the best way to validate whether a particular user has ownership of a website?
Google Website tools allows you to just upload a file with a very specific name. so, you could require that the user create a file in order for you to verify that they own the website
require 'digest/sha1'
require 'net/http'
# you may want to store a unique value in the website table instead
unique_id = Digest::SHA1.hexdigest("#{website.id}/#{website.created_at}")
response = Net::HTTP.start(website.url, 80) {|http| http.head("/verify_#{unique_id}.html") }
website.verified = true if response.code == "200"