My horse did the same thing to me when I tried to bathe him when he was almost about 2. He kept dancing around the tree, even though I started out real slow and easy. He broke the halter! Yeah, it got real muddy and messy and I felt like I was doing more harm then good, he was filthy! It is a gradual process. Start at his feet and let him get used to the sensation. Talk real slow and easy to him. Maybe try taking the hose away just as soon as he stops moving even for a second to reward him for being still by taking the pressure away. Keep doing that until he is comfortable with that and then work your way up to his upper legs and shoulder. It will definitely take time! Hope everything goes well!