For some reason the slo-mo tortoise did not work with this one. I got there in the end, having listened eight times, but it still sounded like "ro-bheaga don" which had me splitting it into "raibh" and an unidentifiable "bheagadon" which set me off after mastodons" and pteranodons*. It's clearly too early in the morning...
Apparently, the new web redesign shows a "turtle" icon even though Irish doesn't have the option of slowing down the audio.
why is there a hyphen?
I learnt from a connemara-native teacher that ró only takes a hyphen when it is followed by a vowel... (unlike an that always comes with a Hyphen)
The entry for ró in the FGB links to 6 examples of ró- with a hyphen, The first 4 involved ró- as a prefix to a word starting with a vowel (ró-ard, ró-éasca, ró-íochtarach and ró-onórach). But the final 2 use a hyphen when the word starts with a consonant - ró-thais and Ró-Naofa.
The NEID entry for "too" provides links to examples in other entries such as ró-bhéalscaoilte, ró-mhórchúiseach, ró-ghortach and ró-leitheadach.
The 2016 version of the Caighdeán includes ró-leisciúil.
In most cases, these sources don't use a hyphen between ró and words that start with a consonant, but there are certainly examples of the hyphen being used by reliable sources. So the hyphen isn't necessary, but it is used at times.