I don't know if there is a more modern alternative but tardak is carried in a preparation which also has a slight sedative effect so the results are not exactly mimicking castration. It is still a good drug to use to help reduce the urge to escape alongside preventative measures and training.
That sounds like what my aggressive-with-other-male-dogs boy had many years ago - he just got fat and lazy, didn't want to do anything. Not a solution for me then, but just the ticket for what you want right now, summermeadows!
Because Moses became a fat slob of a dog on anti-testosterone, I didn't get him castrated then, but many years later I did get him castrated (as he was too much of a handful for friends to look after him when I was away on business.) Over a 12-months period he did calm down on the testosterone-aggression front - but losing his nuts never made him a lazy slob