We got Abby as a rescue about 2 months ago. We believe she is about a year and a half old. Three days ago we gave her an Adams brand flea and tick spot on treatment. Today we found a flea on her.  A friend of ours told us that K9 Advantix is the best stuff to use. Any suggestions or comments about what seems to work and what doesn't?  Also, do you think it would be safe to re-apply another treatment?  Obviously what we have isn't working.  Thanks!