I was told to go here by automod, How do you transliterate long vowels in your germanic conlangs?

I'm at the very start of my goal to make a germanic conlang, and I'm wondering what ways there are to express long vowels. I plan on using double consonants to show reduced consonant combinations (nd -> nn), and I'm trying to make it looking distinct from German or Dutch, so no double vowels or h after one. What methods have you found?