Simplify the following text for a Grade 9 native English-speaking person.
Original: Dependent upon each agency , but generally after completing two years of service , officers may also apply for specialist positions , such as detective , police dog handler , mounted police officer , motorcycle officer , water police officer , or firearms officer ( in countries where police are not routinely armed ) .
Simplified: Some police officers have specialist jobs , such as being a detective , a traffic officer or a dog handler . In some countries , not all police carry guns , so a police officer could choose to become an armed police officer after a lot of experience .