Aggression can be caused by a variety of different factors. Where aggression is purely a result of testosterone - usually male inter-dog aggression - then the implant should have a positive effect on the dog. Therefore, the implants can be used to 'road-test' castration without going ahead with the surgery. If the result is favourable, then the implants can be continued every 6 months or the more permanent castration can be carried out.
As most people know there are no 'quick-fixes' with behavioural problems and they always involve added training, but with the implant (or castration) alone you should expect about a 2/3 reduction in inter-male aggression, a 2/3 reduction in mounting and a 1/3 reduction in urine marking (entire males only). The implants do not have an effect if the males are already castrated.
Hope this helps!