late 14c. (adj.); 1630s (n.), "Any rhyming verse in which the meter is forced into metronomic regularity by the stressing of normally unstressed syllables and in which rhyme is forced or banal" [Miller Williams, "Patterns of Poetry"]. probably from dog (n.) + pejorative suffix -rel and applied to bad poetry perhaps with a suggestion of puppyish clumsiness, or being fit only for dogs. 

As used here and throughout the life of the author, the term is self-deprecative, always accompanied by an eager hope that readers will find the results to be not "bad poetry" but instead too perfect in rhyme and scansion.