If you're reading this guide then I assume you are around level 20 and have a level 4 town hall, and have probably been playing backyard monsters for more than a week. There are probably other people of higher levels in your maproom, who have yards which seem very good, because they protect everything behind a long wall that goes all the way around their yard. Before you decide to copy this idea, consider this: does everything need to be protected? If your yard doesn't protect everything then they bits it does protect will be better protected. So first of all let's find out what actually needs to be protected. The Bits that are important to your yard are things that store and make resources, and things that protect them.
That leaves us with the town hall (TH), the silos, the resource generators (RGs), the towers and crucially the blocks. So before we start building our yard, make sure you have the maximum amount possible of each of these, apart from towers which are way out of your price range such as the Railgun and laser, and possibly the tesla, the bunker and the aerial defense tower (ADTs). Don't worry about them if you can't afford them. It's quite easy to get all the basic towers you have (5 snipers and 5 cannons) and form a very good defense without any of the special towers(although if you can get them it will give you an advantage). Your basic towers should be at level 3 and 4, because this will make them strong enough to one hit kill monsters such as bolts, finks and pokies, which is almost certainly what you will get attacked with the majority of the time at this level. A yard planner will make things easier but its not essential.
Concentrated Fire and Pathing
I now want to introduce the idea of concentrated firepower (CF). This means that if you get your towers closer together they will be stronger than if they were apart. On your yard planner click the button that says "show tower ranges". Each towers range so the closer together your towers arethe better you will be able to kill your enemys monsters. What we need to do now then is make the monsters come to the towers. This is where the blocks come in. You need to use your blocks to chanel monsters towards your towers. There are several ways of doing this, It's upto you how you do it but before you do, there is a prerequisite; a monsterbaiter. With this you can test if monsters will chew through the blocks (bad) or go around them (good) .In my example on the right, monsters have to walk around 28 blocks to get to the main base. (This design is with a level 5 TH but can be done with lower levels). You need to test out exactly how far you can make the monsters walk before they chew through (refresh between each test or results can be inaccurate). It is worth playing around with the length of things monsters are required to path around, and also the distance between the wall and your buildings. When conducting your tests make sure you only change one thing each time and remember that brains and bolts will path further than anything else.
These are your secret weapons, because attackers can't see where they are. When a monster steps on one, or goes within a certain distance, it will explode, dealing high damage to all nearby monsters. Regular booby traps deal 800 damage, and heavy traps do 10,000 damage to ground monsters and 5,000 damage to aerial monsters, but they can only be triggered by Crabs, PX's, Daves, Drull, Gorgo and stage 1 or 2 Fomor. The key to designing a good base is good booby trap placement. This means placing traps where monsters will tread. To work this out we need to get into the mind of the attacker. They will almost certainly do one of three things. The first thing they could do is to attack noobishly, this just means flinging monsters in randomly and hoping for the best. The majority of attacks before zafreeti is unlocked (which is further than this guide is meant to take you) will consist of catapuling the laser(s) a wave or two of octos and/or ichis and then a wave of pokies to finish off. The third form off attack normally found at this level is droping a champ in and hoping he will solo the base. The first and third form of attacks are nothing to worry about unless your attacker has a level 6 drull.