Worming questions

[MBlanchrd@aol.com]

Hi, all,

   I've been worming my two horses every eight weeks.  I've been worming in
the following sequence: ivermectin, ivermectin, rotectin, ivermectin,
ivermectin, rotectin, etc. 
This past week, I was two days late in worming my boys. 
On the day I did worm them,(this time with rotectin),  Jordan had obviously
been rubbing his tail, always a  sign that he needs worming. (damn it, and his
tail was growing out nicely from the LAST time he'd rubbed it....).

My questions are:  In being two days late and Jordan's actions showing worms
(I dind't have a fecal test done), does this mean that the worming schedule is
ineffective? 
By worming, am all I doing is keeping the worms under control, rather than
eliminating them completely? I am assuming that one cannot COMPLETELY
eliminate the worms.

Is it wise for me to perhaps shorten the worming intervals to seven weeks?
Or should I worm only with ivermectin and not rotate with a pyrantel
(spelling) anthelcide? 

Using a feed through, like strongid C, is not an option, by the way.

Any advice would be appreciated.
Michelle and Jordan , who wonders why mom doesn't like his tail looking like a
witches' broom....

.