I have a lot of roosters...lol. If one has ever tried to challenge/spur me, I make sure I get a hold of him quickly and put him down like the roosters do to each other (they'll grab the opposite rooster by his comb) and I'll hold him down firmly with his neck and face one the ground to show him who's boss. I may also peck his head with my finger just to get the extra point across.
Just be careful not to be too rough and injure his neck. This usually shakes them up a bit and they usually think twice before they try it again...lol.
It's in your rooster's best interest to be firm and not let him get away with being aggressive. If it becomes a bad habit, it may be his demise in the end.
Boundaries are a good thing, especially with roosters.
I also blunt most of my roosters spurs. Some people need their roosters to have full spurs to protect the flock so they prefer to leave the spurs. Some people twist them off.
I prefer to blunt my roosters' spurs to the point where the spur begins to get soft and just before it bleeds.
This helps protect the hens from serious injury, it still gives the roosters' a weapon should they ever need it...but it makes it impossible for them to spike me should they ever try.
I use a pair of nail clippers for dogs most of the time. It's very easy to control how much is being cut.
I've also used the serrated hoof trimmers for my sheep on a couple of guys who have spurs too big to fit in the nail clippers.
I would imagine a good pair of side cutters would work too.
