This is somewhat of a long post, just saying.
Remember the the opening scene of the game? When you first started playing? After asking you to enter in the village name, and set up your village, a couple of goblins rush out of the forest and attacked your village. Of course, the cannon took care of them easily, but the real question is: Why do the goblins not attack you anymore after that incident?
My idea is this: How about we let the goblins attack your village, every once and a while, just to add variety to attacks?
Every once and a while, a small army of goblins would rush out from the forest surrounding your base. The goblin army attacking would act as a player of the same TH level, with no loot penalties or bonuses. The attacks would come from randomly selected goblin base in the single player campaign that you may have not raided yet. The randomly selected base can be any one of the stages in the campaign, not only the ones you have already gotten 1 star on. The amount of goblins attacking would be based on the randomly selected goblin base that is attacking you. Farther along in the campaign, the villages are larger and therefore have more goblins to attack you with. Goblins will not be able to attack you while you are online, or while another player is in the process of raiding you. Goblins will be able to raid you during an active shield, as you are able to raid them with your shield on. You will not lose any trophies from a goblin attack, nor gain any. For example:
The probability of you getting attacked from goblins from a select base would be:
Probability = 1 / Amount of goblin bases without full storages/townhall
In the example above, the probability of getting attacked by goblins from the goblin village of "Rocky Fort" would be 1/50, or 0.02%.
Say you did get attacked by goblins from Rocky Fort.
The goblin army would be pretty small and weak, since Rocky Fort is early on in the single player campaign.
The goblins would be randomly placed on any of the sides of your base, and they would function like the normal A.I. of the goblins in your armies, going for the collectors and storages, essentially all of your resources. Your defenses would function as normal, along with your clan castle and heroes. There is no time limit, the battle continues until all the goblins are dead, or your entire base has been destroyed. The loot stolen by the attacking goblins would go into the storages of the goblin village.
In the Rocky Fort attack example, say that the goblins were able to steal 2k of gold and 3k of elixer. That loot would go into the storages of the goblin village. You can then go back and attack that village and steal the loot back.
The formula for finding the amount of goblins that each base gets is:
Amount of attacking goblins = (Your level * Goblin Base Number) / 10
This creates a lower amount of goblins attacking lower level bases, and much more goblins attacking a high level base. The amount and level of goblins would depend on the base that is attacking you, not only on your level. The denominator value can be changed, I just thought it should be ten to balance things out.
The level of the goblins (Like the level from your labs) would be determined by the strength of the goblin base:
Payback - Maginot Line: Level 1 Goblins
Rat Valley - Fool's Gold: Level 2 Goblins
Thoroughfare - Sicilian Defense: Level 3 Goblins
Obsidian Tower - Chimp in Armor: Level 4 Goblins
Faulty Towers - Mega Evil: Level 5 Goblins
Crystal Crust - Sherbet Towers: Level 6 Goblins
The goblin base number would be determined by its place in the single player campaign. For example:
Payback = 1
Goblin Forest: 2
Goblin Outpost = 3
Rocky Fort= 4
Goblin Gauntlet = 5
Cannonball Run = 6
Two Smoking Barrels = 7
....
Sherbet Towers = 50
The numbers above can be changed, it is just my idea for the goblin armies.
When you log on to Clash of Clans, you know how it has that white message board with the attacker's name, level, and trophies won/lost? I think that the goblin's attacks (If implemented) should go up on that board too. Instead of the level, the goblin attack would depict a goblin's head, indicating it was a goblin attack. The name would be the name of the village that attacked you, and the trophies won/lost would just be a slash mark.
The frequency of these attacks would be like the frequency of the obstacles spawning. Maybe an attack every 4 to 8 hours would be sufficient to make these attacks somewhat common, but not so common that they become annoying. Once the storages and town hall of a certain goblin base are full, they will no longer be able to attack you. This will limit the ability of the goblin bases to keep on attacking inactives indefinetely, depriving collector loot from the system. Goblins are greedy, right? So they won't stop looting until they have the maximum amount of loot (When their storages/townhall is full).
This will add incentive to play more of the single player maps, because before they would have no loot after you three starred them, which sort of reduces the willingness of you to attack that base. Now, more loot will circulate between the goblin villages and you, creating more incentive to play the single player campaign and get your loot back. Also, since there is the possibility of being raided by a goblin base that you have not yet unlocked, it will add incentive for you to complete the single player campaign so that you can raid that base. This will not reduce any of the loot floating around in the system, just make it so you have more stuff to do while you have an active shield.
This is not a perfect idea, I would appreciate comments and suggestions.
Thanks guys :)

