checking a string for two instances of ..

[Skaperen]

i get a string foo that will be a problem if there are two or more instances of the particular characters in another string bar. so if bar has 'apz' then foo must not have more than one 'a' and not more than one 'p' and not more than one 'z'/ i'm looking for a small nifty easy to read way to check foo for this.