Hi there,
Horridon is my favorite fight. There's a lot of neat things you can do to up your damage and control.
Survival
http://worldoflogs.com/reports/rt-7x...?s=2674&e=3339
BM
http://worldoflogs.com/reports/rt-7l...?s=3380&e=4042
Here's what my strategy is for this fight:
Spec into lower deterrence CD. If your healers are struggling, deterring dire calls could help a lot.
Choose between Binding Shot and Silencing Shot. If your raid is good on interrupts, go with binding shot; if venomancers/dinomancers are getting casts off, go for silencing shot.
Spec into Thrill of the Hunt. This may lower your DPS in the final phase, but it'll give you cheap multi-shots and free arcane shots if your spirit gets too close.
Spec into Barrage. Glaive Toss may work better, but I don't think it's reliable enough when adds are spread out.
I use AMoC for the single-target boost in the last phase, but it's not particularly important.
For the actual fight:
Keep dots up on all adds with MS if SV. Pretty much spam MS whenever there's more than 2 adds up (read: almost all the time). Unload your single-target abilities (KC, ES) on high-priority targets. Interrupt/stun when it seems like a good idea.
One thing I found out is that using snake trap to deal with the direhorn spirit is super OP for all specs. If you place it correctly and the spirit pops the trap, the snakes will chase after it for FIFTEEN seconds, knocking it back the entire time. By the time it gets back, it'll definitely be off CD again.
Until the final phase, always use explosive trap. This is an AoE fight through-and-through until the last phase.
In the last phase, just switch to a normal single-target rotation, making sure to use snake traps to keep your add away.
The last major decision you need to make will be when to use readiness/stampede. Since your DPS is low, you will probably greatly exceed 10 minutes, so you could theoretically use readiness three times, and this would be a DPS gain; however, there may be specific parts of the fight you're struggling with, which may require you to save it so you only use it twice. If you use it at the start, it will probably be up by the middle of the frost door, and again **after** Jalak is dead.
EDIT: Oh, and one last thing. I keep my pet on assist. If you're SV, it might be okay to leave it on Horridon, though it's a bit greedy.