Yesterday I found myself near Elwynn Forest, so I thought it would be a good time to pick up the Stormwind half of the Fishing Diplomat achievement.
I've found that ever since they changed the entry guards to be lvl 75 rather than 65, sneaking in through the front door is a no-no; even with +stealth trinkets working overtime, they see right through it. My Vanish only has about a 50% chance of getting them off my back. Instead I've discovered that the best way to get into Stormwind is to come the back way through the new harbor around back. You can swim there from the Westfall/Elwynn border, and the guards are all lvl 65. Keep in mind that fishing from Stormwind Harbor does NOT count toward your Fishing Diplomat achievement; you have to apparently fish from inside the city walls for the achievement to take.
I was able to stealth to the canals without much problem and grab my single catch. Since I was already in SW and the Deeprun Tram was not that far from me, I figured I'd take my chances at Old Ironjaw.
Stealthing to the tram was not a problem; I think there was a single guard I had to avoid on the way. Once I got into the tram I opted to run the rails rather than take the tram, as I was still flagged and I didn't want to draw unnecessary attention to myself.
I came out at Ironforge in Tinkertown, which is very close to the Forelorn Cavern. This was indeed much better than coming through the front door! This way I'd have to deal with at most 5 lvl 75 guards rather than the score or so that I'd have to deal with from the front entry. However 5 guards was about 5 more than I wanted to deal with!
I mounted up and started to make a mad dash toward the cavern. Sure enough, the first pair of guards aggroed me. I then rode straight into the middle of the second pair, and picked up their aggro as well. I was almost to the cavern when they dismounted me, so I dropped a Vanish and prayed. I got the message "Leaving Combat" and breathed a sigh of relief.
About one second later I encountered the fifth guard, whom I had not counted on. This guard pats the wall directly across from the cavern entrance. If I'd stuck to the south wall there's a very good chance I could have avoided him. I knew I was going to die but I figured I'd at least do it in a good position. So I ran for the water and managed to swim about halfway across the pool before I got killed.
After that, it was easy. I did the necessary corpse-run, edged myself against the south wall, did a /sleep command to bring a low profile, and started fishing.
At first I had the place entirely to myself. After a couple of minutes a Human Paladin showed up and I started to get worried; I really didn't want to fight anybody, I just wanted a nice pacifist fishing trip. After a few seconds he waved at me and proceeded to fish by my side. Awesome.
Every couple of minutes another Alliance character would ride by the pool. Most didn't even see me, but some would stop and look at me for a few seconds and then ride on. I only had one character try to pick on me, a Draenei Shaman. My solution to this was to Vanish and then move to another spot. He tried to locate me again but with no luck, and eventually went away. I then unstealthed and proceeded to start fishing again, and the two people who'd showed up there to fish cheered as I reappeared. What a great thing: cameradery between the factions, and all because of fishing!
Finally (after about 150-200 throws) I got my prize - Old Ironjaw. The two other fishermen cheered me again, I took a bow, and I hearthed the heck out of there.
In a nutshell, it's very possible and not that hard, as long as you come in through the back door at Stormwind and take the Deeprun Tram. Most people will ignore you (at least they did me) as long as you stick to fishing and don't try to fight anybody. If you are attacked it may even be best to take the blows and not fight back so that when you return the people who witnessed the battle know that you're not interested in fighting, just fishing.