If it is keyless:
1) Put key in sleep mode (Example:
Quick Key Fob Tips - Heffner Toyota)
2) Pull metal key from the key fob
3) Leave fob in the car in hidden place
4) Lock car using sensor on the handle
5) Do what you want to do (swim, etc) while keeping metal key with you.
6) Open vehicle using metal key
7) Activate key fob back, put metal key inside key fob