Your answer would be that the participle phrase "barking in the yard" modifies dog.
Explanation:
The complete participial phrase in the sentence above is "barking in the yard for hours". In this case, the participial phrase is present so it ends in -ing. Since all phrases requiere two or more words, a participial phrase will include objects and/or modifiers. What is more, participial phrases always function as adjectives, adding description to the sentence. As you can see, the participial phrase in question modifies the noun <em>dog. </em>Moreover, this participial phrase is essential as the information it provides is considered relevant to complete the meaning of the sentence; it helps identify which dog the speaker is referring to. If it was removed, the meaning of the sentence would be changed. The sentence would refer to that particular dog no longer (see 1).
