Don't lose on defense? :)

Do you mean the weekly reset? 

No, there's no way to stop that if that's what you mean. 

ok thenks, it just seems that the next day my arena status drops down and i have to do battles just to get where i was the previous day

There are 2 things that happen:

1. Other players fight the team you have set for defense, if they beat it, you lose points.

2. Once per week (8am UTC monday if my time zone adjustment is right) arena resets, and rewards are given out based on which tier you finished in