I did it in a notepad, so maybe you will have to correct the syntaxis:

trigger AccountSVOC on Account (before insert, before update, after update) 
{
	//BEFORE SECTION
	if(trigger.IsBefore)
    	{
		Set<String> svocs = new Set<String>();
		Map<String, Account> accountsBySvoc = new Map<String, Account>();

		for(Account a: Trigger.new) 
		{
			if(a.SVOC__c != null){
				if(svocs.contains(a.SVOC__c)){
					//We have 2 different records with same SVOC in the trigger!
					throw new MyException('ERROR MESSAGE');	
				}
				svocs.add(a.SVOC__c);	
				accountsBySvoc.put(a.SVOC__c, a);		
			}
  		}

		List<Account> accounts = [Select SVOC__c From Account Where SVOC__c IN :svocs];
		if(accounts.size() > 0){
			//can be repeated
			if(trigger.IsInsert){
				//are repeated for sure
				throw new MyException('ERROR MESSAGE');			
			}else{
				//check if it not the same record
				for(Account a :accounts){
					Account triggerAccount = accountsBySvoc.get(a.SVOC__c);
					if(a.ID != triggerAccount.ID){
						//Is not same object, It's repeated
						throw new MyException('ERROR MESSAGE');	
					}				
				}
			}
		}
    	}
	else
	//AFTER SECTION
	{

	    List <SVOC__c> SVOCs = new List <SVOC__c> ();
	   
	    System.debug('Chris in trigger');

	    for(Account a: Trigger.new) 
	    {
		System.debug('Chris in account loop');
		if( (a.SVOC__c != null ) && (a.SVOC__c != Trigger.oldMap.get(a.Id).SVOC__c) )
		{ 
		    System.debug('Chris in status changed');
		    SVOC__c SVOC = new SVOC__c ();
		    SVOC.Account__c = a.Id;
		    SVOC.SVOC_ID__c = a.SVOC__c;

		    System.debug('Chris creating new SVOC and adding to list');
		    SVOCs.add(SVOC);
		}
	    }

	    if(SVOCs.size()>0)
	    {
		System.debug('Chris has values to insert = '+ SVOCs.size());
		try{
		    insert SVOCs;
		}catch (System.Dmlexception e)  
		{
		     system.debug (e); 
		}
	    }
	}
}

 It's make sense to you?

PD: You will need to create a class "MyException" (or whatever) extended from Standard Exception Class