Dogs in mosque

In the name of Allah, the most Beneficent, the most Merciful.

Answer

Saaiduna Abu Talha Radiallahu Anhu reports that the Prophet of Allah Sallallahu Alahi Wasalam said, “Angels do not enter a house where there is a dog or pictures.”  (Sahih Bukhari p.880 v.2)

According to the Hanafi Fiqh, the body of a dog is not impure, rather its saliva is.  (Raddul Muhtar p.382 v.1)

With regards to your question, the trustees of the mosque should prevent the police in entering or checking the mosque with dogs.  If they do come in by force then the carpet will not become impure by the dogs walking on it.  However, if the saliva touches the carpet or any other area then it will be necessary to remove it.   One should wash the area until the body of the impurity is removed.  (Nurul Idah p.59) 

Only Allah Knows Best

Mohammed Tosir Miah

Darul Ifta Birmingham