"dominant" miniature schnauzer

[Nat]

We have two mini schnauzers, a 9 year old spayed female, "Freya", and a neutered 4 year old male, "Loki." Last year our daughter came back home from 4 years in Montreal with her male (intact) boxer, "Zion". We were a little worried about the safety of having Zion in the house with our little dogs. It turns out, however, that Zion, against all logic, lets Loki rule him. This seemed "cute funny" at first, but, Loki now seems to think he can, and should, try to dominate any big dog. While on an off-leash run in an informal dog park out of town he decided that he would run up and "take over" a pack of four German Shepherds. The only thing that saved his life was the owner of the Shepherds intervening. Loki had some serious bite wounds, but,with prompt vet care, he was soon as good as normal. We had hoped he would have learned his lesson - that Zion is not the same as other big dogs and he had better show proper respect. Alas ! such is not the case. Not only does he continue to dominate the boxer but when out walking ( on the leash) he still wants to take off after any big dogs we encounter. Dogs his size or smaller don't seem to interest him as much.

Any suggestions on how to get him to realize his life depends on NOT trying to dominate other big dogs?: confused: