With the exception of certain permanently protected facilities, such as the White House, the practice used at Mar-a-Lago is no different than that long-used at any other site temporarily visited by the President or other Secret Service protectees.
While the Secret Service does not determine who is permitted to enter the club, our agents and officers conduct physical screenings to ensure no prohibited items are allowed onto the property.
On March 30, 2019, physical screening was conducted by the Secret Service once Mar-a-Lago staff determined an individual was to be granted access to the property. After the first physical screening, Mar-a-Lago staff transported the individual by a shuttle to the next screening checkpoint. Individuals are prohibited from disembarking the shuttle between screenings and the route is monitored by Secret Service personnel.
After undergoing screening at the second Secret Service checkpoint the individual, per club protocol, was immediately met by club reception. The Mar-a-Lago reception staff then determined that the individual should not have been authorized access by their staff and Secret Service agents took immediate action resulting in the arrest of the individual.
-- United States Secret Service
Source: U.S. Secret Service