This is just a draw out of many games, I don't think this is the start of a declining run for Arsenal. Just because they lost two points doesn't mean Arsenal will lose the rest of the games ahead. On the contrary I think the team will bounce back in the next game and get a win to stay at the top of the table. It was a tough game for Arsenal against Southampton and I'm not surprised that the game ended in draw
There is a difficult match awaiting Arsenal in November where Arsenal will meet Chelsea. I started considering Chelsea in the last few match because their form has improved. Chelsea are unbeaten in 9 match so far including in the Champions League, so I hope the match vs Arsenal will be one of the match that will really jeopardize Arsenal's position at the top.
I think Nottingham Forest, who will play Arsenal this week, also know Arsenal's strengths. They may have prepared a strategy to stop Arsenal's dominance in that match, so it's always possible for another disappointing result before Arsenal meet Chelsea.