"Secure confinement" refers to keeping someone or something safely and securely enclosed or restricted, usually to protect others or prevent harm. Full definition
The cat needs to stay in secure confinement for the first 2 - 3 weeks so that it becomes familiar with and identifies with its new location. (routthumane.org)
After a short period of secure confinement, the cats will accept your barn as their new home. (barncats.org)
After a short stay in secure confinement, the cats will accept their new home and be chasing mice out of your grain with enthusiasm! (nbcats.org)