Monitoring and enforcing Hall County codes regulating short-term vacation rentals on Lake Lanier has proved a growing challenge, according to some local officials and residents. And a study committee of state lawmakers is reviewing regulating and taxing Internet-based travel accommodations such as Airbnb, VRBO and other rental websites. The county Marshal’s Office recently opened an investigation on a Lanier home located on Northlake Road that had been operating as a short-term, vacation rental without proper permitting.