I dont think you can completely "fix" it and stop yourself from using it in the future. I guess the best method would be to make sure those around you (family, t, pdoc) know what the plan is / was in detail so they can hopefully see some signs and stop you acting on it in the future. And the meds that you plan on using that arent yours can be hidden by the person who owns them maybe?

As for the date this time - can you plan something fun involving others for that day?

I have had a plan and a date and I know that even when you have come out of the depression that date it hard to resist but personally I made myself really busy with other people on that day and it was easier that way.