Ivermec and Safe Guard do not treat the same group of worms. If you are alternating these wormers you are treating some worms while allowing others to run out of control.
Wow, this is an old thread, but what heck, I'll reply.
According to studies, when the proper dose of ivermectin is given, it's not likely to treat anything other than large roundworms, but if large enough doses are given, and I mean *large*, it will treat most other worms. IMO, don't waste your money on it, just buy Safeguard (Fenbendazole) or Valbazen (albendazole), have routine fecals done, and work with a vet.
-Kathy