...and DEFINITELY the buddy awareness issues.
I've been entangled by both fishing line and kelp (though never both at once, yet) and usually it's not too difficult to untangle myself, or cut myself out with my trauma shears. Sometimes I have been aided by my buddy, other times I could do it myself.
However, one time when I was in a kelp forest in California, I was bringing up the rear in a 3-person buddy team (which is not my ideal buddy situation to begin with, but there was an odd number of divers that day.) One of the divers was a novice, so we put him in the middle of the line so that the other diver and I would both be close to him. My tank valve got caught, and I couldn't go forward. I tried to signal to the other two with my light, but it was daytime and visability was pretty good, and I guess my light didn't stand out enough to catch their attention. They kept swimming forward, and rounded a bend in the rockwall to which we were swimming parallel.
I couldn't untangle myself, so I reached for my trauma shears to cut myself out. I was having a hard time finding/reaching the strand of kelp that needed to be cut, and wondering why my buddies had not returned to see where I was. Eventually I was able to twist my arm/back/shoulder into the configuration needed to cut that rogue kelp thread. I'm pretty flexible, and it still wasn't easy to do, but I did manage to get out. I went to catch up with my buddies, and met them as they had just turned around to search for me.
What had happened was that the experienced diver in front had been regularly signalling to the novice diver between us, who SHOULD have checked on me. Before I got tangled, I had been staying close to him, and had also been signalling frequently with the novice diver. When I no longer signalled to him (because I was trapped,) he apparently didn't realize that if I don't catch him and signal to him, it is his job to turn around regularly and signal to me. So the lead diver was signalling to the novice, who should have been signalling to me, but wasn't, and always just gave the OK sign to the lead diver, who thought that the "OK" had been passed down the line to me and back up, when it hadn't. When they reached a more open area, the lead diver saw that I wasn't behind the novice, and headed back (with the novice) to look for me.
If I hadn't managed to free myself, my buddies would have made it back to me before I ran out of air, but the whole thing could have been avoided if we had done better emphasizing buddy communication and awareness when we briefed the dive originally. Buddies are not perfect, but they are still your best defense against peril once the dive is underway. A good pair of trauma shears on one side of your body and a small knife on the other side are also great things to protect yourself from kelp and line alike.