Any suggestions?

me my brother and his friend are thinking of starting a dog walking buisness. i am 13 and the other 2 are 10 and 9. we are having it 3-5 dollars, because we dont want to be too expensive. actully the cost is dependent on the size of the dog. i think its a good idea because the 3 of us are saving up for something... but now i am a little worried because what if something happenes? like what if something happenes to the dog? we are going through with it, but are there any good suggestions out there that couold help us? please share, and no smart alec remarks! thanks alot! :)