It's not funny. Marriage in your backyard is also valid.
No, a marriage in a backyard is USUALLY invalid because this will USUALLY involve defect of form, i.e., one or both persons are Catholic and are attempting marriage before a non-Catholic witness without dispensation and will often involve invalid consent and/or vows.
These days many divorced Catholics will say that they received an "anullment" when , in fact, what was received was an ecclesiastical acknowledgement of defect of form.
On the flip side, defect of form, while invalidating, can be easily corrected through a process of sanation (regularising the marriage back to its defective start) or convalidation (having the parties presently exchange proper consent and vows before a proper ecclesiastical witness).
A decree of nullity (or recognition of validity) is a canonical ruling in a formal matrimony case before a tribunal. A decree of defect of form does not require a formal matrimonal case and can usually be determined prima facie by the civil marriage license or non-Catholic wedding certificate.