dogs are not allowed on the sand, and even if some are spotted taking their pets on the beach, this is no license to follow the bad example, especially by a foreign visitor - keeping these simple rules in mind will allow any tourist to know what to do while at the beach, and understanding more of what goes on around them.  

wise beach behavior includes not taking anything of significant value to the beach for general safety reasons - sunblock is vital to protect one's health and should be a practice utilized every day even when clouds are in the sky - renting an umbrella between the hours of 11:00 -15:00 is highly recommended as the tropical sun is most intense at these times

a great book of details regarding rio de janeiro's beach normalcies is 'a carioca - guia de estilo para viver a Cidade Maravilhosa' which is translated to a carioca way - style guide to enjoy the marvelous city - this collection addresses fashion tips, beauty, and etiquette and is available in app form, downloadable via this link on i-tunes.