I would recommend getting a squirrel call and then learning to use it at the right times. Below I've copied a post I made a couple years ago (on a different forum) about squirrel calling.
I have used squirrel calls for over 10 years and have had some good success with them. The best advice I can give you is to only use a squirrel call when you are having trouble locating squirrels. When you bark on a squirrel call, you will get one of two responses: 1) the squirrels will go to a high point on a tree and silently scan the woods for the location of the noise, 2) the squirrel will bark back at you aggressively. I have only had the squirrel bark back at me twice...ever. But, it is a pretty cool experience. Generally a squirrel bark will put the squirrels on a little higher alert and it's tough to spot them moving. But using the call is effective when you can't locate any squirrels because they will tend to come nearer to the call, even if they try to sneak in on the sound.
If you use a bark call, couple it with a squirrel distress call. Haydel's makes a call that is a two-in-one. Best squirrel call I've ever used. More mature squirrels will often respond to a squirrel distress call rather than a bark call. Rustle some leaves as you blow the squirrel distress call. Again, they will try to sneak in on the call, but once they are interested, it's tough for them to ignore the sound. I've bagged more squirrels without a call than with one, but a call adds a new dimension to your hunting that is tough to beat. If you do get a bark call, go to haydel's website and listen to the way they use the call, the rhythm they use is the most effective one I've heard.