With BS fishing and the multiple types of spam there are ways around it; but there is one ever-existing tactic that's hard to beat: Ganking.
Whatever tactic a player uses, it takes some immense amount of skill and/or dirty tricks to come out on top of two or three guys pounding on you. Whether host or invader, you're likely to get ganked if you invade in a lot of the more PvP-oriented areas. (Forest, Anor Londo.)
I've seen mountains of complaints, some I've made myself, about looking for some fair PvP and getting circle-backstabbed by someone and their buddies; but there's never much you can do to stop it except hope that everyone just decides to play fair. (Ha.)
The DLC is a good chance to incorporate something to prevent ganking. I fantasize about From putting out some sort of phantom-neutralizing spells in the future. There are plenty of directions for such a thing to go in, but I was thinking about a spell that paralyzes or weakens a host's phantom friends; or maybe one that makes an invader immune to damage from anyone but the host. Such a thing would force a host into a 1v1 match.
And I haven't forgotten about hosts that get ganked in the Forest/Anor Londo. I've been double teamed by Forest Kitties and Gwyndolin's Pets enough times for me to know that invaders aren't the only ones that have it tough. For hosts about to be mutilated by two invaders, I'd suggest a spell neutralizes one of the invaders, thus bringing back to a fair 1v1 once more.
Of course, these are rough ideas I just spat out, and I realize that the chances of my ideas actually coming into effect ever are rather nonexistent; but a guy can dream, right?
What about you guys? Any thoughts?