Scanning the inscription of The Classical High School of Tampere

Question

I strolled around Tampere today, and I noticed an inscription in the wall of The Classical High School of Tampere:

FENNIA VOS GENUIT
GREMIO VOS INTIMA FOVIT.
ARBORIS AUSCULTET
MURMURA QUISQUE SUAE.
FENNI VOS MANEATIS.
AT HOC ANIMIS RETINETE
GRAECIA QUID DEDERIT
VOBIS ET HESPERIA.

This raises a couple of questions. Let me focus on scansion here; I might return to other issues later. (Anyone is free to ask questions about the content, of course!)

This is inscription contains quite obviously two elegiac couplets; the line breaks match the caesurae. I have two questions regarding scansion in comparison to classical Latin:

1. It appears that hoc is intended to be hŏcc (neuter singular) instead of the ablative hōc; at least I see no support for an ablative. I recall that it has been mentioned on this site before that hoc can be pronounced this way, but I forget where. Are there classical examples where hoc is clearly neuter nominative or accusative (not ablative) but scansion requires that the c is long like in this poem?
2. I have learned that vōbīs always has two long vowels, but the i appears to be short here. Is there classical precedent for such a short i in vobis or nobis?

(If you think these questions should rather be asked separately, I'll be happy to do so. I'm not sure what's best.)

Since this might be of local interest, let me repeat the question briefly in Finnish: Tampereen klassillisen lukion seinässä on piirtokirjoitus, joka on kirjoitettu elegisellä säeparilla. Miten sanat hoc ja vobis on tarkoitus ääntää, ja vastaako se klassista runomittaoppia? Katso yksityiskohdat yltä.

Answer 1

Hoc

There is indeed classical precedent to pronounce hoc as hocc. Velius Longus in De Orthographia 53 writes:

At cum dicimus 'hic est ille', unum c scribimus et duo audimus, quod apparet in metro. Nam:

Hoc erat alma parens, quod me per tela, per ignes
eripis…
(Aeneis 2.664–665)

Si unum c hanc syllabam exciperet, acephalus esset versus nec posset a longa syllaba incipere, quae est heroico metro necessaria. ergo scribendum per duo c 'hocc erat alma parens' aut confitendum quaedam aliter scribi,
aliter enuntiari.

That is, in hic est ille we write one c but we hear two. This is made evident in the quoted verse from the Aeneid: the hoc has a double c although it is not written. Velius remarks that one should write hocc erat alma parens or accept that some things are written differently from their pronunciation.

Vobis

I went through all occurrences of vobis and nobis in Vergilius. There were plenty of cases when they appear before a vowel, making the quantity of the second vowel clear. All cases point to a long i.

Perhaps scanning the i short is modeled after brevis brevians or iambic shortening, but that would require the preceding syllable to be short (light). It is not clear whether this is a slip, conscious poetic license, or something else, but I would consider it a mistake in classical verse.