Hi, Brittany,
Unfortunately, if a client searches without putting in exact dates they will still find you. It's not your responsibility to get back to them; it's their fault for not looking at your schedule.
If you do not want to be contacted at all for a while you can mark yourself as 'away' - they will then receive an automated message that says something to the effect of "this sitter is away and may not respond right away." (At this time, you can't specify start an end dates when marked "away".)
Though I know it's frustrating to be contacted for dates you have already marked as unavailable, I do find it handy. Sometimes people's plans are a little flexible or, if there is overlap with another client on one end, I can still make things work (with permission from all parties involved, of course). Also, even though I'm not available for THOSE dates, maybe we can set up a Meet and Greet for the future.
The thing that really makes me roll my eyes is when I am contacted for, say, a 10-month old Labrador Retriever puppy, starting tomorrow - when my profile clearly states 1) I don't take puppies 2) I don't take dogs over 40 pounds 3) I'm not available 4) - though this is not clearly visible - I don't take any clients without a M&G first. :-)
Good luck!