Certain old penniless escort on an ’orse (10)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

A charade of GUAR[d] (‘escort’) minus D (‘old penniless’) plus ‘an’ plus [s]TEED (h’orse’, with the apostrophe indicating the dropping of the first letter, not, as is usual, specifically an H).