Any tips? I have tried for the past 2 hours over and over and have yet to be able to get the fountain more than 60% of the way down before I run out of resources and run out of troops to hold off the onslaught.
"In order to make an apple pie from scratch, you must first create the universe." - Carl Sagan
I always destroy the large enemy base on Easy/Moderate. On Hard I just drop off about six mortars on one of the small islands near the fountain, have them bombard it along with the fixed gun while my navy/land units protect it.
Here's how to destroy the large Boneguard base on Easy/Moderate, - (Copy and paste from AgeComm)
I can never manage to destroy it on Hard. On easy, and moderate it's possible it just takes a ton of management(30 Lancers, 30 Xbows, 2 Falconets(Home Shipment, wait till you're nearly at population cap because of other units/villager pop then overpopulate with this card), and 4 Mortars. Split the lancers/xbows into smaller attack groups so you don't focus fire every single unit on just one enemy soldier.). Usually I can have the base destroyed before Alain ever appears.
If you've got free ship cards use the mortars to destroy the outposts along the coastline of the large base(the south eastern gate into the fort), and then park ships along the coast to provide support(don't try to attack by sea, or use a double pronged attack they fail miserably). Try to keep your units out of the many towers line of fire, using your mortars to destroy them from a distance and the rest of the attack force on defense until the number of outposts is reduced. Until you learn what to expect you can pretty much assume the first attack will ultimately fail to destroy the base, but it will cripple it letting a second wave finish it off.
The fixed gun is best bolstered in my experience by placing a few mortars on either side, and building docks nearby. My fort is generally built east of the starting location, near the small strip of land forming a bridge from the large base to your side of the lake, capped on each end by two towers(4 towers total). One or two towers should be built near your starting dock, that's where the large base drops off raid groups transported by ships.
If you're having trouble getting good cards, you can leave a particular mission running(such as the Ottoman Fort) for several hours to jump your home city level up. Build a wall near the south western native village(on the ottoman fort mission), to cut off the only access point into the biggest part of the map(build your TC near their fishing operation). While attacking the Ottoman Fort send villagers to steal the resources they have access to outside of your walled up half of the island.
The biggest problem with this strategy is the fact you can't arrange your deck, and once an age fills up with cards it starts pushing the ones at the right side offscreen making them unable to be shipped each time you pick a new card for that age. So you have to be careful picking cards, and will never pick the full number of cards you have available.
Once you kill the base, and Alain you are free to linger and soak up unlimited experience or fortify the lake as you see fit. Even with the threat gone, you still can't keep the fountain for yourself and have to destroy it to proceed.
If you target the fixed gun on the fountain, and there are no enemies left to attack it cannot be stopped from attacking the fountain.
Even when the enemy docks are destroyed, ships will "magically" spawn but at a much slower rate letting you simply park ships there for free kill experience when a caravel appears every 4-5 minutes. This is identical to how the first battle against pirates plays out, except in that case it is Fishing Boats that appear every 4-5 minutes despite the lack of an enemy dock.