You have a limited amount of time before Furion comes under attack so you must move swiftly. This is the most critical time of this mission. If you make haste here and get your base running and pumping out units as fast as you can you'll have time to make a few mistakes later on. Begin immediate construction of an assault force (I took three dryads, four huntresses and four Archers along with Tyrande as well as two ballistae in a second group) and take the only path out of your base. That is to the east. So this is an easy to defend place. Take your forces out the eastern side of your base and take the first northern turn you can. This will lead to a group of murlocs you can kill (destroy the hut for boots of speed) and, beyond, a goblin merchant. Go back to the path and head further east and take the next northern path you come across. You're likely to encounter an orc party here. And surely will as you approach the fountain of health. Fortunately, though you may take some losses this is a good place to regroup and reinforce them.

Now we move further on to the north where you will find the orc base. Use your ballistas to destroy the watch towers and send your other units in to begin doing some major damage when it's safe. Use the ballistas to deal some good damage to the enemy units while the others distract them. This base is not too difficult to conquer. When you've finished every last orc you can now cross the stream to the north and begin your attempt to destroy the primal guardians. Note that since the orcs are gone you don't need anything to defend your base - throw everything you have at these guardians!

Follow the path. There are no diversions here. Your only goal is to finish those guardians and get to Furion. The first guardian is level 6 and is somewhat tough. He's protected by small owlbears who will attack you so prepare for a rougher battle than you may have expected. I recommend you have at least 3 dryads for this as they can dispel his sleeping spell. There is a jade ring past this first guardian in a crate you can break. I didn't even bother picking it up even though it's +1 agility. Tyrande has nice equipment already. The second is also level 6 and is almost identical to the first except he has larger owlbears. The biggest problem with these guys is enduring the attacks and being able to press forward. I recommend trying to keep a steady stream of units flowing out of your base and to the north. Hell, set the rally point of both of your military buildings up there if you like. The final one is a little harder than the last and has the same owlbears protecting him.. You must kill the owlbears as well as the guardian in order to succeed. Good luck. When you're done, take your hero to the pedestal with the horn and the mission is complete.