As has been said previously, just set an alarm on your phone for 10 minutes or so prior to SAR expiry. Simple and effective.
I have forgotten to cancel SAR a few times in the past and have had a call from the SAR centre asking politely whether I was safe. These gracious people always accept my groveling apology and even refrain from laughing.
I find it a bit hard to accept that 25 SAR cancellations are missed per day.