2 years old is when cats reach 'social maturity' and the point when a younger cat is likely to challenge the alpha cat for position. Is Fudge the alpha cat (or was she the alpha when you only had two?). It sounds as if he is constantly trying to establish his hierarchy.
The other possibility is that Fudge has something going on medically that may be in initial stages that you haven't detected symptoms, but Jasper has. Cats are a survival of the fittest type animal and the healthy ones may attack the weaker ones. If you have any suspicions of Fudge having something medical going on, you probably ought to get her to a vet to be checked out.
Assuming Fudge is OK physically. One thing you can do it put a collar with a bell on Jasper. Then Fudge will always know where he is and have some advance warning of his approach. She won't get surprised.
You might want to read Cat vs Cat by Pam Bennett-Johnson (or Johnson Bennett...I can never remember which order and I'm too lazy to get my butt off the couch to go look for the book
). This is a book on managing a multi-cat household. I learned a lot from it.
I have a similar situation with Kobi, he's a very lagre (17 lbs) dominant male and finds it necessary to flex his muscle on a regular basis. I would try punishment tactics with him (time outs, witholding of attention immediately after an incident etc.). Didn't seem to have much impact. Then there was a thread here a few weeks ago where someone suggested that attacking the other cats was a bid for attention and even negative attention was better than no attention. So the recommendation was to first to catch the offender thinking about causing an incident, deflect him and immediately shower him with attention. I've been taking that approach and it actually seems to be working better. I've also been making sure to give him some extra one on one attention...he loves to be brushed and instead of once a week, I now brush him for just a few minutes every morning...not very long at all, but that really seems to make him happy.
I hope some of this helps....