Documentation is a key element in protecting yourself.
Assuming you are performing to the language of the contract, you need to document everything you do on all of your sites. Especially important is what you do to document deicing activities. Time on and off the site, the amount of product distributed and when you checked the site (or performed "ice watch" activities) are a few of the items that need recorded. Sidewalk work on any site (if part of your contract responsibilities) should also result in detailed activity reports. Savvy investigations during the discovery process will request such documentation to determine if your activities on the site were appropriate and sensible. Often, the first discovery request will cover the date of the incident. Subsequent discovery requests will ask for your records a week prior and a week after the date of the incident. Why? The plaintiff’s legal team is seeking to determine if records are consistent and not manufactured after the fact for the incident date. This is important for determining credibility of the contractor's record-keeping system.
Was the material applied appropriate for the conditions at the time? This can be determined from the records. Are your people properly trained? This, too, can be ascertained from company records. Did you use the appropriate amount of material for the conditions at the site? Check the records. Was the equipment properly calibrated for the material being distributed? Again, check the records. If the customer is an "on-call" deicing customer, do you keep track of when calls come in for service? What they are looking for are exact times. Good contractors keep track of every single call that comes into their office. Often, you will get a call to deice a parking lot 15 minutes after the slip-and-fall occurs. With no consistent records, you will have difficulty proving you were not involved.
Records. Records. Records. You cannot have enough.