Qualifying for residency via a rental

Hi,

I want to make myself eligible to apply for residency, preferably around Llanca, Catalonia. I am just about up to signing up for a rental but of course Llanca is very touristy so long-term rent is difficult. The one I like, for example, is for 8 months. The agent was concerned that this would not be long enough contract to convince the authorities. Of course, she DOES want to sell me something instead. 

I see no sign on sites to do with seeking residence about any stipulations as to length of rental contracts. What do people think?

cheers, Judy