Why was Rexie the dog kept in the enclosure in the garden?

Rexie still bites people after eight years like when he was two years old.-found from two areas in the story.on the top of page 90, we realise that rexie is about 8 - 10 years old:when younger, he had bitten a few nervous servants and visitors. since then, for the past eight years, he had to spend the days in the enclosure under the pomegranate tree which offered little shade from the blazing afternoon sun.and on the bottom of page 91, we realise what is rexies behaviour till today:rexie was still the fierce two-year-old; he had bitten; he was not to be trusted again despite aging teeth, weak eyesight and the clumsiness of old age.