Hi Sabrina
Years ago I bred Jack Russell's and had 2 dogs and 3 bitches, the dogs used to fight quite a lot and pee on guests boots, coats etc - when I say pee they were marking really, it became a real problem so I had the dogs neutered as I was lead to believe this would help the situation - by this point my dogs were age 7 and 5 years. It didn't change a thing!
and I caught the younger dog trying to mate with his mother and sister!! so they both still had tendencies too!
However my son got a Jack Russell dog 5 years ago and we had him neutered at 8 month old we've never had a problem with him, he doesn't fight, mark or have tendencies but my son says it's made him homosexual as he has been caught mounting our bassett hound dogs head if a bitch is in season, which really is quite funny, he never goes anywhere near a bitch in season though!
I did think about getting Mika spayed but I have successfully run dogs and bitches together for many, many years with no problems - perhaps because we've always lived very remote and don't have the problem of straying dogs from close neighbours, the guy who owns the collie dog actually drove to the farm and let his dog out of the pickup and wonder round our farm, he could see Mika was in season and stood and watched the dogs "do it"!!
I'm sure you can imagine the neighbour and I no longer speak and cross words were exchanged!!