Answer by Professional Japanese Teacher
Issyookenmee hataraitekurete arigatoo.
You can use “Gokuroosama” when you wish to reward or appreciate your subordinates. Be careful as this phrase sounds rude if a subordinate uses it on his superior. Adding “desu” to “otsukaresama” will make it polite.
A superior can say “Otsukaresama” to his subordinates. The “Isshookenmee” in “Issyookenmee hataraitekurete arigatoo” is used to praise someone for being serious and earnest.
Your subordinates will surely feel pleased if you praise them like that.