Hi there, I agree with the previous answer! Neutering is definitely good thing. It reduces/stops territorial marking, may improve aggressive/dominating behaviour, and removes the risk of any tumours in the dog's bits.
I got our Collie done when we moved house, as he began to mark, and displayed super-nervous behaviour that didn't improve (even more than usual!) He was about 16 months, there were no complications whatsoever.
We took him to the Vet first thing in the morning, and they called us mid-afternoon to let us know he was fine and we could collect him. Other than being a bit subdued for the evening, he was absolutely fine!
We were advised to take it easy with him for a few days, gentle walks on the lead and no stressful scenarios etc.
He has since stopped marking, calmed down and is still my boy! A lovely mix of grown-up dog and absolute puppy!
Of course, I have met people who say that neutering made no change to their dog's behaviour whatsoever, but the majority say otherwise, and even if that's the case, it is a better option for health (and safety!) reasons.
Best bet is to have a chat with your Vet. Some vets neuter your dog for �25 through Dogs Trust if you're on certain benefits.
Lisa :)