This doesn't sound good, "Client must understand that we may experience difficulties that are out of our control, and may not be able to make it to your property on schedule sometimes." How about just making a statement, "We may not be able to make to your property as scheduled sometimes due circumstances beyond our control, weather etc.
Just wondering to about the lawn maintenance specifications, do you mow without trimming, edging and blowing. I can't imagine anyone wanting their property mowed but not trimmed, edged and blown. Also, do you want to service a customer "twice per month" or biweekly? They are two different things. Just wondering.
I like the form posted by Delong. You may want to look into that.