דברים ג,יא: כִּי רַ ק- לֶּזְׁרַּב שֶּרֶּע ֹו שְׁרַע הֵּּנִה םיִאָפְׁרָה רֶּתֶּ יִמ רַאְׁ שִנ ןָ שָּבַה ךֶּלֶּמ גֹועהֲלֹה הִוא
Baal HaTurim notes that "Halo" (it is not) is always spelled with an Alef at the end, as it is a combination of the word "lo," (no) and the prefix questioning Hei. Here it is spelled with a Hei in place of the Alef to create a word whose numerical value is 40. This alludes to the fact that in the future a king who will reign for 40 years will again reclaim these lands, King Dovid. As well the letter Hei is used to allude to King Dovid who is five generations down from his ancestor Salmone (Boaz, Oveid, Yishai, Dovid).
Alternatively, it alludes to Moshe who captured it from Og. Moshe was 10 cubits tall, jumped 10 cubits, and held a sword that was also 10 cubits tall. The total height of all this is 30 cubits and Moshe struck Og in his ankle, which was 30 cubits above the ground (see Berachos 54b). Moshe was Hei-Hei cubits tall and he struck Og at Lamed height, therefore HaLoH.
